[BUGFIX] Fix date format in code templates

Removes also a wrong trailing slash in CompatibilityTest

Resolves: #56476
Releases: 6.1, 6.2

Change-Id: If684a2d075800e4b39cd1fec3a3cb205190cfdb7
Reviewed-on: https://review.typo3.org/27978
Reviewed-by: Nico de Haen
Tested-by: Nico de Haen