[BUGFIX] Ensure cache tags are strings in workspaces

On SQLServer you cannot insert integers in varchar
columns therefore the workspaces module ajax requests
are failing and you cannot use the module.

Cast the workspaceId to a string before using it as a
cache tag.

Change-Id: I0827dd6dddd9203fb7846934a034b826a515cdf3
Resolves: #82901
Releases: master
Reviewed-on: https://review.typo3.org/54535


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>