tests: ignore __pycache__ directory when finding input files

This should fix a race condition seen in CI.

Author: indygreg

tests/common.py

@@ -149,7 +149,9 @@ def random_input_data():
         return _source_files
 
     for root, dirs, files in os.walk(os.path.dirname(__file__)):
-        dirs[:] = list(sorted(dirs))
+        # We filter out __pycache__ because there is a race between another
+        # process writing cache files and us reading them.
+        dirs[:] = list(sorted(d for d in dirs if d != '__pycache__'))
         for f in sorted(files):
             try:
                 with open(os.path.join(root, f), "rb") as fh: