Add Kokoro test filtering for MacOS/Windows
diff --git a/tools/run_tests/python_utils/filter_pull_request_tests.py b/tools/run_tests/python_utils/filter_pull_request_tests.py
index 032c070..4ad9812 100644
--- a/tools/run_tests/python_utils/filter_pull_request_tests.py
+++ b/tools/run_tests/python_utils/filter_pull_request_tests.py
@@ -128,7 +128,7 @@
   # Get file changes between branch and merge-base of specified branch
   # Not combined to be Windows friendly
   base_commit = check_output(["git", "merge-base", base_branch, "HEAD"]).rstrip()
-  return check_output(["git", "diff", base_commit, "--name-only"]).splitlines()
+  return check_output(["git", "diff", base_commit, "--name-only", "HEAD"]).splitlines()
 
 
 def _can_skip_tests(file_names, triggers):