[Python] Fix race condition in requirements cache creation (#37042)

* Fix race condition in stager.py when starting
multiple pipelines concurrently (fixes #36847)

* remove race condition test

Author: NayanMathur411

sdks/python/apache_beam/runners/portability/stager.py

@@ -218,7 +218,7 @@ def create_job_resources(
            is None) else setup_options.requirements_cache)
       if (setup_options.requirements_cache != SKIP_REQUIREMENTS_CACHE and
           not os.path.exists(requirements_cache_path)):
-        os.makedirs(requirements_cache_path)
+        os.makedirs(requirements_cache_path, exist_ok=True)
 
       # Stage a requirements file if present.
       if setup_options.requirements_file is not None: