[BUGFIX] Remove invalid button attribute

This merge request removes the autocomplete attribute of the login
button.

Resolves: #92619
Releases: master, 10.4
Change-Id: I6a2ba3e82c87f261fa7415f7124c70b657e7d3a3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66317


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>