Added an admin flag to the repository bumper workflow merge action

[rauldpm]

Description

This PR adds the --admin flag to the merge action of the repository bumper workflow due to the restriction applied to the numbered branches, as currently the following error is preventing the automatic merge

X Pull request wazuh/wazuh-qa-automation#2215 is not mergeable: the base branch policy prohibits the merge.
To have the pull request merged after all the requirements have been met, add the `--auto` flag.
To use administrator privileges to immediately merge the pull request, add the `--admin` flag.

This change has been tested with the wazuh-qa-automation repository https://github.com/wazuh/wazuh-qa-automation/pull/2218

[fdalmaup]

LGTM