[aws unit test utils] only create a recordings directory when the env var is set (#45752)

* Only create placebo recording test directories when the environment variable PLACEBO_RECORD is set
(cherry picked from commit 5467ac3454)

test/units/utils/amazon_placebo_fixtures.py

@@ -61,6 +61,10 @@ def placeboify(request, monkeypatch):
         # remove the test_ prefix from the function & file name
     ).replace('test_', '')
 
+    if not os.getenv('PLACEBO_RECORD'):
+        if not os.path.isdir(recordings_path):
+            raise NotImplementedError('Missing Placebo recordings in directory: %s' % recordings_path)
+    else:
         try:
             # make sure the directory for placebo test recordings is available
             os.makedirs(recordings_path)