CI: allow non-standard signature

Make allow to use non-standard signature such as 'Co-authored-by:'.

Signed-off-by: TOKITA Hiroshi <[email protected]>

Author: soburi

.github/workflows/checkpatch.yml

@@ -27,4 +27,4 @@ jobs:
         fetch-depth: ${{ env.PR_FETCH_DEPTH }}
     - name: Run checkpatch review
       uses: webispy/checkpatch-action@v9
-
+      env:  CHECKPATCH_COMMAND:  ./zephyr/scripts/checkpatch.pl