Use --set-bot-commit instead of --tbrs to avoid self-approval

TBRs are no longer allowed, so update how we create the LKGM
commit to use the Bot-Commit label.

BUG=chromium:1176924
TEST=manual

Change-Id: Ibd76419a43313d20398f075b8d2f19ec2768330c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2688179
Commit-Queue: Sean McAllister <smcallis@google.com>
Tested-by: Sean McAllister <smcallis@google.com>
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/chrome_committer.py b/lib/chrome_committer.py
index b315a05..abf9ad6 100644
--- a/lib/chrome_committer.py
+++ b/lib/chrome_committer.py
@@ -100,7 +100,7 @@
       # not part of the shallow checkout, -f to skip editing the CL message,
       upload_args = self._git_committer_args + [
           'cl', 'upload', '-v', '-m', self._commit_msg, '--bypass-hooks', '-f',
-          '--tbrs', constants.CHROME_GARDENER_REVIEW_EMAIL]
+          '--cc', constants.CHROME_GARDENER_REVIEW_EMAIL, '--set-bot-commit']
       # Marks CL as ready.
       upload_args += ['--send-mail']
       if self._dryrun:
diff --git a/lib/chrome_committer_unittest.py b/lib/chrome_committer_unittest.py
index 6411efc..ddc6e1e 100644
--- a/lib/chrome_committer_unittest.py
+++ b/lib/chrome_committer_unittest.py
@@ -85,7 +85,8 @@
                                 'cl', 'upload', '-v', '-m',
                                 'Automated Commit: Modify OWNERS and BUILD.gn',
                                 '--bypass-hooks', '-f',
-                                '--tbrs', 'chrome-os-gardeners@google.com',
+                                '--cc', 'chrome-os-gardeners@google.com',
+                                '--set-bot-commit',
                                 '--send-mail', '--use-commit-queue'])
 
   def testUploadDryRun(self):