[BUGFIX] Avoid invalid mktemp argument busybox in cglGit

The busybox variant as packaged with the test images based on
alpine of mktemp needs six 'X' as template in cglFixMyCommit.sh.
It otherwise emits a warning executing the command:

 > Build/Scripts/runTests.sh -s cglGit

Resolves: #96432
Releases: main, 11.5, 10.4
Change-Id: I1c1853aabe79186694161c21f5fe0341e1bd2e75
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72874


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>