fix: stop returning 400 code when user installs github app

[joseph-sentry]

Purpose/Motivation

Sometimes when a user tries to install the github app (on self-hosted), they will encounter a 400 response

Links to relevant tickets

Fixes: codecov/engineering-team#806

What does this PR do?

• change return of get_redirection_url_from_state to tuple
• if second element of tuple is False, it means that the state was not set and we should redirect to the dashboard without logging the user in

[codecov-staging]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[codecov-qa]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c8657da) 95.98% compared to head (919cc12) 95.98%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #314   +/-   ##
=======================================
  Coverage   95.98%   95.98%           
=======================================
  Files         612      612           
  Lines       15794    15798    +4     
=======================================
+ Hits        15160    15164    +4     
  Misses        634      634           

Flag	Coverage Δ
unit	95.98% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	95.98% <100.00%> (+<0.01%)	⬆️

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[codecov-public-qa]

Codecov Report

Merging #314 (919cc12) into main (c8657da) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #314   +/-   ##
=======================================
  Coverage   95.98%   95.98%           
=======================================
  Files         612      612           
  Lines       15794    15798    +4     
=======================================
+ Hits        15160    15164    +4     
  Misses        634      634           

Flag	Coverage Δ
unit	95.98% <100.00%> (+<0.01%)	⬆️
unit-latest-uploader	95.98% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
codecov_auth/views/base.py	99.49% <100.00%> (ø)
codecov_auth/views/github.py	98.13% <100.00%> (+0.03%)	⬆️
codecov_auth/views/gitlab.py	98.41% <100.00%> (+0.05%)	⬆️