[Chore] Fix autoupdate commit author

Problem: Currently scheduled job commits use the last real committer as
author instead of serokell-bot.

Solution: Set serokell-bot as commit author.

.github/workflows/update.yml

@@ -19,5 +19,6 @@ jobs:
         with:
           commit_user_name: serokell-bot
           commit_user_email: [email protected]
+          commit_author: serokell-bot <[email protected]>
           commit_message: "Update nixfmt input"
           file_pattern: "flake.lock"