fix(nextcloud_test): Really handle docker container port already being allocated

[provokateurin]

#2770 wasn't actually working because the exit code was always 0 due to detached mode.
By checking if the container is still running we really know that everything is fine.
I tested this by lowering the range of random ports to 20 so failures are very likely and it managed to properly find a port for each container.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.09%. Comparing base (fcb36bd) to head (deec18b).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2781      +/-   ##
==========================================
+ Coverage   28.88%   29.09%   +0.20%     
==========================================
  Files         373      373              
  Lines      138192   138192              
==========================================
+ Hits        39923    40211     +288     
+ Misses      98269    97981     -288     

Flag	Coverage Δ		*Carryforward flag
account_repository	98.47% <ø> (ø)
cookie_store	99.48% <ø> (ø)		Carriedforward from 6925096
dashboard_app	96.05% <ø> (ø)
dynamite	31.05% <ø> (ø)		Carriedforward from 6925096
dynamite_end_to_end_test	61.75% <ø> (ø)		Carriedforward from 6925096
dynamite_runtime	85.40% <ø> (ø)		Carriedforward from 6925096
interceptor_http_client	97.18% <ø> (ø)		Carriedforward from 6925096
neon_dashboard	96.05% <ø> (ø)		Carriedforward from 6925096
neon_framework	59.34% <ø> (ø)
neon_http_client	94.32% <ø> (ø)
neon_notifications	100.00% <ø> (ø)		Carriedforward from 6925096
neon_rich_text	100.00% <ø> (ø)
neon_storage	94.66% <ø> (ø)
neon_talk	99.45% <ø> (ø)		Carriedforward from 6925096
nextcloud	24.59% <ø> (+0.23%)	⬆️	Carriedforward from 6925096
notifications_app	97.36% <ø> (ø)
notifications_push_repository	98.11% <ø> (ø)
sort_box	90.90% <ø> (ø)		Carriedforward from 6925096
talk_app	98.84% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

see 2 files with indirect coverage changes