make the githubv4.URI -> *githubv4.URI on AvatarUrl

[patrickdevivo]

fixes a nil pointer exception that was occurring on this column

[codecov-commenter]

Codecov Report

Merging #203 (2d048fb) into main (f965a1c) will decrease coverage by 0.04%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main     #203      +/-   ##
==========================================
- Coverage   69.52%   69.47%   -0.05%     
==========================================
  Files          44       44              
  Lines        2228     2231       +3     
==========================================
+ Hits         1549     1550       +1     
- Misses        436      437       +1     
- Partials      243      244       +1     

Impacted Files	Coverage Δ
extensions/internal/github/repo_prs.go	75.80% <50.00%> (-0.70%)	⬇️

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