[TASK] Integrate InstallTool acceptance suite into Backend suite

The acceptance test suite for the stand alone install tool can
easily coexist with the other backend related tests, there is
no good reason for the overhead of a separate suite. So it gets
merged into the backend suite.

Resolves: #93621
Releases: master, 10.4
Change-Id: I460596985cd992c4f7d59df989c7992590e479d8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68158


Tested-by: core-ci <typo3@b13.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Richard Haeser <richard@richardhaeser.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Richard Haeser <richard@richardhaeser.com>