[TASK] Add ext:install to unit test suite

Change-Id: I24d7fc1afdfb7badc7126e31c554dac34b89eb0b
Resolves: #47467
Releases: 6.1
Reviewed-on: https://review.typo3.org/20097
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring