[BUG] refine maven release configuration

[line-o]

Describe the bug

During the last two releases

• git tags were created (6.0.0 and 6.0.1)
• one GitHub release was created (v6.0.0)
• 4 additional assets were attached to the single GitHub release (6.0.0 XAR and jar and 6.0.1 XAR and jar)

Expected behavior

The last two releases should have

• created two git tags (v6.0.0 and v6.0.1), beginning with the letter v
• created two GitHub releases (v6.0.0 and v6.0.1)
• each GitHub release should have only one additional artifact attached, the XAR

Additional Context

The subsequent patch release happened after the default branch was renamed to main. It is possible that this affected the second release which was performed from the same clone as before.
Instead of running all commands GitHub recommends to run after this operation only the new main branch was checked out.