chore(serverless): remove flaky mark from two serverless tests [backport 3.4] (#13111)

Backport 612d802 from #13039 to 3.4.

This PR addresses two flaky tests in
`tests/contrib/aws_lambda/test_aws_lambda.py`. The issue that needed
fixing was that env vars are checked during patch/unpatch. Since unpatch
was being called after the env was reset, they were never being
unpatched correctly. This PR ensures that the patching and unpatching
occurs within the env override.

## 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: Rey Abolofia <[email protected]>

Author: github-actions[bot]

tests/contrib/aws_lambda/test_aws_lambda.py

@@ -1,3 +1,5 @@
+import contextlib
+
 import pytest
 
 from ddtrace.contrib.internal.aws_lambda.patch import patch
@@ -11,7 +13,6 @@
 from tests.contrib.aws_lambda.handlers import manually_wrapped_handler
 from tests.contrib.aws_lambda.handlers import static_handler
 from tests.contrib.aws_lambda.handlers import timeout_handler
-from tests.utils import flaky
 from tests.utils import override_env
 
 
@@ -46,13 +47,15 @@ def get_env(env=None):
     return {**common_env, **env}
 
 
-@pytest.fixture(autouse=True)
-def setup():
-    yield
-    unpatch()
+@contextlib.contextmanager
+def override_env_and_patch(env):
+    # patching and unpatching must be done while the environment is set
+    with override_env(env):
+        patch()
+        yield
+        unpatch()
 
 
-@flaky(1744053478)
 @pytest.mark.parametrize("customApmFlushDeadline", [("-100"), ("10"), ("100"), ("200")])
 @pytest.mark.snapshot
 def test_timeout_traces(context, customApmFlushDeadline):
@@ -64,9 +67,7 @@ def test_timeout_traces(context, customApmFlushDeadline):
         }
     )
 
-    with override_env(env):
-        patch()
-
+    with override_env_and_patch(env):
         datadog(timeout_handler)({}, context())
 
 
@@ -83,9 +84,7 @@ def test_continue_on_early_trace_ending(context):
         }
     )
 
-    with override_env(env):
-        patch()
-
+    with override_env_and_patch(env):
         datadog(finishing_spans_early_handler)({}, context())
 
 
@@ -98,11 +97,8 @@ async def test_file_patching(context):
         }
     )
 
-    with override_env(env):
-        patch()
-
+    with override_env_and_patch(env):
         result = datadog(handler)({}, context())
-
         assert result == {"success": True}
 
 
@@ -117,11 +113,8 @@ async def test_module_patching(mocker, context):
         }
     )
 
-    with override_env(env):
-        patch()
-
+    with override_env_and_patch(env):
         result = manually_wrapped_handler({}, context())
-
         assert result == {"success": True}
 
 
@@ -135,7 +128,6 @@ async def test_module_patching(mocker, context):
     ],
 )
 @pytest.mark.snapshot
-@flaky(1744053478, reason="Did not receive expected traces: 'aws.lambda' for [handler3-instance_handler_with_code]")
 def test_class_based_handlers(context, handler, function_name):
     env = get_env(
         {
@@ -144,8 +136,6 @@ def test_class_based_handlers(context, handler, function_name):
         }
     )
 
-    with override_env(env):
-        patch()
-
+    with override_env_and_patch(env):
         result = datadog(handler)({}, context())
         assert result == {"success": True}