ci: fix flaky tracer tests (#13616)

Currently the tracer `iast_enabled` setting is not properly reset in
tracer tests, causing some subsequent tests to fail with errors like:
```
FAILED tests/tracer/test_writer.py::test_writer_api_version_selection[AgentWriter-darwin-None-None-False-v0.5_1] - AssertionError: assert 'v0.4' == 'v0.5'
  
  - v0.5
  ?    ^
  + v0.4
  ?    ^
```
This PR fixes it.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Co-authored-by: Brett Langdon <brett.langdon@datadoghq.com>

Author: vitor-de-araujo

tests/tracer/test_propagation.py

@@ -376,7 +376,7 @@ def test_asm_standalone_minimum_trace_per_minute_has_no_downstream_propagation(
         finally:
             with override_env({"DD_APPSEC_SCA_ENABLED": "0"}):
                 ddtrace.config._reset()
-                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 @pytest.mark.parametrize("sca_enabled", ["true", "false"])
@@ -421,7 +421,7 @@ def test_asm_standalone_missing_propagation_tags_no_appsec_event_trace_dropped(
         finally:
             with override_env({"DD_APPSEC_SCA_ENABLED": "0"}):
                 ddtrace.config._reset()
-                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 def test_asm_standalone_missing_propagation_tags_appsec_event_present_trace_kept(tracer):  # noqa: F811
@@ -455,7 +455,7 @@ def test_asm_standalone_missing_propagation_tags_appsec_event_present_trace_kept
         # Ensure span is user keep
         assert span._metrics["_sampling_priority_v1"] == USER_KEEP
     finally:
-        tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+        tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 @pytest.mark.parametrize("sca_enabled", ["true", "false"])
@@ -514,7 +514,7 @@ def test_asm_standalone_missing_appsec_tag_no_appsec_event_propagation_resets(
         finally:
             with override_env({"DD_APPSEC_SCA_ENABLED": "false"}):
                 ddtrace.config._reset()
-                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 def test_asm_standalone_missing_appsec_tag_appsec_event_present_trace_kept(
@@ -562,7 +562,7 @@ def test_asm_standalone_missing_appsec_tag_appsec_event_present_trace_kept(
         assert span._metrics["_sampling_priority_v1"] == USER_KEEP
 
     finally:
-        tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+        tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 @pytest.mark.parametrize("upstream_priority", ["1", "2"])
@@ -631,7 +631,7 @@ def test_asm_standalone_present_appsec_tag_no_appsec_event_propagation_set_to_us
         finally:
             with override_env({"DD_APPSEC_SCA_ENABLED": sca_enabled}):
                 ddtrace.config._reset()
-                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 @pytest.mark.parametrize("upstream_priority", ["1", "2"])
@@ -700,7 +700,7 @@ def test_asm_standalone_present_appsec_tag_appsec_event_present_propagation_forc
         finally:
             with override_env({"DD_APPSEC_SCA_ENABLED": sca_enabled}):
                 ddtrace.config._reset()
-                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False)
+                tracer.configure(appsec_enabled=False, apm_tracing_disabled=False, iast_enabled=False)
 
 
 def test_extract_with_baggage_http_propagation(tracer):  # noqa: F811