fix: allow to use an entreprise GIthub instance and an authentication token in the same time again

[foyerunix]

Hello,

This PR fix a regression introduced in #21292.
Before that, we were able to use both an URL and also an authentication token.

Best Regards.

[bunnyshell]

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[crenshaw-dev]

Should this be unit tested?

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@0484f9f). Learn more about missing BASE report.
Report is 27 commits behind head on master.

Files with missing lines	Patch %	Lines
applicationset/services/pull_request/github.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #23129   +/-   ##
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  Coverage          ?   60.05%           
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  Files             ?      343           
  Lines             ?    57887           
  Branches          ?        0           
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  Hits              ?    34766           
  Misses            ?    20339           
  Partials          ?     2782           

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[foyerunix]

Hello @crenshaw-dev,

I tried hard to implement an unit test without changing the definition of the NewGithubService function.

First I tried to check if the URL and the token were correctly set by inspecting the internals of the http.Client, but I couldn't correctly test for the token and it was brittle. Then I tried with a test HTTP server, but I couldn't make it work this way also.

Therefore I ended adding an optional http.Client argument to the NewGithubService function, this let me mock the Transport so I can inspect both the URL and the token.

Best Regards.

[olivergondza]

I confirm this fixes the bug. The code looks good to me as well...