Fix API to use author for commits instead of committer

[6543]

There is a bug in modules/convert.ToCommit where the committer is used in place of the author.

This PR fixes this.

[codecov-commenter]

Codecov Report

Merging #16276 (f017071) into main (9a0cd3a) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main   #16276      +/-   ##
==========================================
+ Coverage   45.40%   45.42%   +0.01%     
==========================================
  Files         709      709              
  Lines       83484    83484              
==========================================
+ Hits        37910    37919       +9     
+ Misses      39495    39481      -14     
- Partials     6079     6084       +5     

Impacted Files	Coverage Δ
modules/convert/git_commit.go	87.70% <100.00%> (ø)
modules/indexer/stats/db.go	42.85% <0.00%> (-7.15%)	⬇️
models/repo_list.go	77.04% <0.00%> (-0.78%)	⬇️
modules/notification/mail/mail.go	38.23% <0.00%> (+1.96%)	⬆️
modules/queue/workerpool.go	56.48% <0.00%> (+2.67%)	⬆️
models/unit.go	43.83% <0.00%> (+2.73%)	⬆️
services/mailer/mail_comment.go	85.18% <0.00%> (+7.40%)	⬆️

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