tools: fix permissions for merve update script

Add execute permission for `tools/dep_updaters/update-merve.sh` so that
the "Tools and deps update" workflow can run it.

PR-URL: #62023
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: richardlau