Fix Terraform::Runner.available?

The endpoint for opentofu-runner ping is just `/ping` not `/api/ping`

Author: agrare

lib/terraform/runner.rb

@@ -9,7 +9,7 @@ class << self
       def available?
         return @available if defined?(@available)
 
-        response = terraform_runner_client.get('api/ping')
+        response = terraform_runner_client.get('ping')
         @available = response.status == 200
       rescue
         @available = false