[BUGFIX] Broken layout for tabs in ExtensionManager

Correct the CSS style of the tabs in the ExtensionManager.

Change-Id: I2078575db684cc826138dce50571cb97f0d653a9
Resolves: #62671
Releases: master
Reviewed-on: http://review.typo3.org/34252
Reviewed-by: Felix Kopp <felix-source@phorax.com>
Tested-by: Felix Kopp <felix-source@phorax.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>