pw_presubmit: Allow relands in commit message fmt

Allow Gerrit-generated relands in the commit_message_format check.

Example of a commit message that would now pass:
https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/112172/2

Change-Id: I95aaa817d692516a206fe0797cd1468fa4f9f385
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/112212
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
index 10c9208..bab0290 100755
--- a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
+++ b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
@@ -756,6 +756,13 @@
         _LOG.warning('Ignoring apparent Gerrit-generated revert')
         return
 
+    # Ignore Gerrit-generated relands
+    if ('Reland' in lines[0]
+            and 'This is a reland of ' in git_repo.commit_message() and
+            "Original change's description: " in git_repo.commit_message()):
+        _LOG.warning('Ignoring apparent Gerrit-generated reland')
+        return
+
     errors = 0
 
     if len(lines[0]) > 72: