Get default branch of repo from GitHub api before downloading a GitHub dependency

[ehennestad]

Fixes bug where default branch had to be explicitly specified in the requirements file.

Before (requirements.txt):

https://github.com/ehennestad/MatBox@main

After (requirements.txt):

https://github.com/ehennestad/MatBox

[github-actions]

Test Results

21 tests   21 ✅  21s ⏱️
 5 suites   0 💤
 1 files     0 ❌

Results for commit 900ceee.

[codecov]

Codecov Report

Attention: Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.

Project coverage is 43.15%. Comparing base (b323a59) to head (900ceee).
Report is 41 commits behind head on main.

Files with missing lines	Patch %	Lines
...x/+setup/+internal/+github/+api/getDefaultBranch.m	72.72%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
+ Coverage   41.11%   43.15%   +2.03%     
==========================================
  Files          53       59       +6     
  Lines        1182     1409     +227     
==========================================
+ Hits          486      608     +122     
- Misses        696      801     +105     

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