ci(all): ignore code diffs introduced by test script (#3545)

internal/kokoro/continuous.sh

@@ -107,7 +107,7 @@ exit_code=0
 
 if [[ $KOKORO_JOB_NAME == *"continuous"* ]]; then
   # Continuous jobs only run root tests & tests in submodules changed by the PR
-  SIGNIFICANT_CHANGES=$(git --no-pager diff --name-only $KOKORO_GIT_COMMIT^ | grep -Ev '(\.md$|^\.github)' || true)
+  SIGNIFICANT_CHANGES=$(git --no-pager diff --name-only $KOKORO_GIT_COMMIT^..$KOKORO_GIT_COMMIT | grep -Ev '(\.md$|^\.github)' || true)
   # CHANGED_DIRS is the list of significant top-level directories that changed,
   # but weren't deleted by the current PR. CHANGED_DIRS will be empty when run on master.
   CHANGED_DIRS=$(echo "$SIGNIFICANT_CHANGES" | tr ' ' '\n' | grep "/" | cut -d/ -f1 | sort -u | tr '\n' ' ' | xargs ls -d 2>/dev/null || true)