[BUGFIX] Fix class name of success button in the install tool

Releases: master, 8.7, 7.6
Fixes: #83044
Change-Id: I2c16f160a18f4c0e58b87261b59fbde90aca2f82
Reviewed-on: https://review.typo3.org/54693


Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>