[BUGFIX] Use correct warning icon in time tracker

The icon_warning2.gif is used instead of the deleted icon_warning.gif.

Resolves: #57116
Releases: 6.2
Change-Id: I3a902a0bfb362c29e8ff6b384b844bf1f7f63cf8
Reviewed-on: https://review.typo3.org/28575
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn