fix package_name_check

Author: chingor13

.github/workflows/generated_files_sync.yaml

@@ -170,6 +170,7 @@ jobs:
         # the rest        : the same as above
         invalid_files=$(find . -name '*.java' \
             |grep --invert-match 'java/com/google' \
+            |grep --invert-match 'javatests/com/google' \
             |grep --invert-match samples \
             |grep --invert-match grafeas \
             |grep --invert-match 'cloud-build.*v2' \