ci: Rename commit message trigger command (#6788)

Rename the internal command used to trigger the commit message
generation workflow. The previous command, /gemini-commit-message,
was causing conflicts or being unintentionally picked up by internal
Gemini code assist tools. The new command, 
/generate-commit-message,  is more generic and resolves this issue.

Bug: 436660675
Change-Id: Ifcb9d2865087073385f0d6de9413303f94e40a7b

Author: zhongqiliang

.github/workflows/gemini-commit-message.yml

@@ -9,8 +9,8 @@ on:
 jobs:
   generate_commit_message:
     # This condition ensures the workflow only runs if the comment is on a PR
-    # and the comment body is exactly '/gemini-commit-message'.
-    if: github.event.issue.pull_request && github.event.comment.body == '/gemini-commit-message'
+    # and the comment body is exactly '/generate-commit-message'.
+    if: github.event.issue.pull_request && github.event.comment.body == '/generate-commit-message'
 
     # The workflow will run on the latest version of Ubuntu.
     runs-on: ubuntu-latest