Handle insecure and ports in go get

[zeripath]

If a gitea running on non-standard port is listed as the location for a go mod file, go will fail to get it as the port is not listed and for HTTP the --insecure flag is not set. This PR applies these changes.

Fixes #6985

Also fixes a similar unreported bug in url.IsExternalURL on non-standard ports.

[codecov-io]

Codecov Report

Merging #7041 into master will decrease coverage by <.01%.
The diff coverage is 13.33%.

@@            Coverage Diff             @@
##           master    #7041      +/-   ##
==========================================
- Coverage   41.46%   41.45%   -0.01%     
==========================================
  Files         442      442              
  Lines       59611    59623      +12     
==========================================
+ Hits        24715    24716       +1     
- Misses      31665    31676      +11     
  Partials     3231     3231

Impacted Files	Coverage Δ
modules/context/repo.go	56.66% <0%> (-0.34%)	⬇️
modules/context/context.go	52.02% <0%> (-2.2%)	⬇️
modules/util/url.go	70.27% <100%> (+0.82%)	⬆️

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