[stable10] install testing app for federation server in CI tests

[individual-it]

backport #32410

[codecov]

Codecov Report

Merging #32411 into stable10 will decrease coverage by <.01%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             stable10   #32411      +/-   ##
==============================================
- Coverage        62.8%    62.8%   -0.01%     
  Complexity      18759    18759              
==============================================
  Files            1220     1220              
  Lines           73470    73470              
  Branches         1279     1279              
==============================================
- Hits            46146    46143       -3     
- Misses          26944    26947       +3     
  Partials          380      380

Flag	Coverage Δ	Complexity Δ
#javascript	53.11% <ø> (ø)	0 <ø> (ø)	⬇️
#phpunit	63.86% <ø> (-0.01%)	18759 <ø> (ø)

Impacted Files	Coverage Δ	Complexity Δ
apps/encryption/templates/settings-admin.php	88.23% <0%> (-5.89%)	0% <0%> (ø)
apps/encryption/lib/Session.php	98.03% <0%> (-1.97%)	22% <0%> (ø)
lib/private/Files/Storage/Wrapper/Encryption.php	67.81% <0%> (-0.25%)	156% <0%> (ø)

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[individual-it]

closing in favour of #32413

[individual-it]

reopening as discussed in the chat as #32413 has more general issues to be solved

[patrickjahns]

temporary solution - for now 👍