[BUGFIX] linkvalidator: Add missing CSS class to "Toggle all" label

This commit adds a missing `form-check-label` CSS class to the label
element of the "Toggle all" field in the backend module of
EXT:linkvalidator to have pointer cursor there as well.

Resolves: #103452
Releases: main
Change-Id: I471a0607f6a3ce4c9c603aee59b0619a4d54cbf9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83558


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Benjamin Franzke <ben@bnf.dev>