[TASK] Enable acceptance tests again

Bring back backend acceptance test execution as pre-merge
and nightly tests. They are hopefully more stable now and
we'll test if they survive the hard pre-merge load without
being too flaky..
The patch changes the bamboo plan specs accordingly but disables
a couple for FormEngine related detail tests that need further
investigation.
The patch also fetches a new patch level of testing-framework
to have proper ac path definition of the ac splitter script:

composer update typo3/testing-framework

Change-Id: Iffcfd60391ba60d5ab2196a00a5bd0a4a93fff7f
Resolves: #85599
Releases: master
Reviewed-on: https://review.typo3.org/57635


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>