[BUGFIX] Use correct class in T3Editor save hook

After merging the Template related sysexts the save hook in T3Editor
needs to refer to the new class.

Change-Id: I6eb4eef2d703b9e50246b7faef808985f609cb7f
Resolves: #50013
Releases: 6.2
Reviewed-on: https://review.typo3.org/22289
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert