BugFix(SDKError): Correct error formatting in SDKError __str__ method… (#1588)

… (#1587)

### BugFix: Correct error formatting in SDKError.__str__

#### Problem
Calling `str(SDKError)` raised the following runtime error:
`looker_sdk.error.SDKError: <exception str() failed>`

This happened when the SDK attempted to convert the error to a string,
which failed due to a malformed generator expression or naming conflict
during the formatting of `self.errors`.

#### Fix
Updated the loop variable in the generator expression from `error` to
`error_details` to:
- Avoid potential name shadowing.
- Improve clarity and correctness of the `__str__` implementation.
- Resolve the runtime error so the error can now be printed correctly.

#### Notes
- The variable `error_details` represents a single instance; per PEP 8,
we may later rename it to `error_detail` for readability.

Co-authored-by: Kiran R <71453237+kiran2706@users.noreply.github.com>

Author: drstrangelooker

python/looker_sdk/error.py

@@ -82,7 +82,7 @@ def __str__(self):
     documentation_url: {self.documentation_url}
     error_doc_url:     {self.error_doc_url}
     error details:
-    {sep.join(str(error) for error in self.errors)}
+    {sep.join(str(error_details) for error_details in self.errors)}
     """