allow U2F with default settings for gitea in subpath

[techknowlogick]

credit to @zeripath for logic

Fix #10231
Likely fixes #5143

[codecov-commenter]

Codecov Report

Merging #12990 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12990      +/-   ##
==========================================
- Coverage   42.59%   42.58%   -0.01%     
==========================================
  Files         671      671              
  Lines       73625    73625              
==========================================
- Hits        31363    31356       -7     
- Misses      37183    37195      +12     
+ Partials     5079     5074       -5     

Impacted Files	Coverage Δ
modules/setting/setting.go	47.61% <100.00%> (ø)
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
modules/indexer/stats/db.go	43.47% <0.00%> (-17.40%)	⬇️
services/pull/check.go	33.84% <0.00%> (-13.85%)	⬇️
modules/indexer/stats/queue.go	64.70% <0.00%> (-11.77%)	⬇️
modules/git/utils.go	73.77% <0.00%> (-3.28%)	⬇️
modules/git/repo.go	46.19% <0.00%> (-1.53%)	⬇️
models/pull.go	54.54% <0.00%> (-0.63%)	⬇️
models/error.go	35.19% <0.00%> (+0.33%)	⬆️
models/notification.go	66.66% <0.00%> (+0.90%)	⬆️
... and 6 more

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[techknowlogick]

Blocking this as it needs more testing.

[zeripath]

Looking at the settings code it is definitely the case that the AppSubURL does not have a terminal "/" and it is always the case the the AppURL has a terminal slash - therefore the proposed PR is correctly stripping off the AppSubURL