[BUGFIX] Wrong comment in ActionMenuViewHelper

ActionMenuViewHelper contains a wrong example for the usage
of the viewhelper. It uses a '=' where a ':' would be correct.

Resolves: #58166
Releases: 6.2, 6.1
Change-Id: I135310be0ac2e8df59f81dfbf694a0febbcde99a
Reviewed-on: https://review.typo3.org/29646
Reviewed-by: Kay Strobach
Tested-by: Kay Strobach
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind