[chore] remove user no longer has errornous behaviour

[Kharonus]

What are you trying to accomplish?

• removing edge cases from code base

What approach did you choose and why?

• updating NC 28 to NC 29 allows removal of user from its last group
• removed special handling from tests

[brunopagno]

What happens if a customer wants to keep using nextcloud 28? Would they become blocked of upgrading openproject if that's the case?

[mereghost]

What happens if a customer wants to keep using nextcloud 28? Would they become blocked of upgrading openproject if that's the case?

IIRC our integrity checks would report it as "non-compatible".

[Kharonus]

uhm, maybe we should bump the min NC version then? :D good idea, will ask @dominic-braeunlein

so, dominic:

• shall we bump the supported min NC version to 29.0.9? In 15.1? This was the version I used for testing the group user removal.
• we only have checks for versions of our integration app and group folder app
  • we could add a check for NC version, too
  • we could add the supported version of NC to our integration app (e.g. version 2.7.2 is supporting only 29 and up)

[Kharonus]

All in all, I'd take the version discussion out of this PR, which basically just amends the tests. no prod code changes. WDYT?