Refactor Git HTTP throttling exclusion logic into helper method
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## Summary
Refactor the Git HTTP throttling exclusion logic in `lib/gitlab/rack_attack/request.rb` to improve code readability by extracting it into a dedicated helper method.
## Background
In !213141, we added logic to exclude Git HTTP requests from the authenticated web throttle. The implementation works correctly but could be more readable when viewed outside the context of the MR.
## Proposal
Move the exclusion logic into a helper method named `exclude_git_http_from_web_throttling?` and use that method in the throttle configuration. This will make the code more self-documenting and easier to understand.
## Related
- !213141 - Original implementation
- #581142 - Parent issue
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/213141#note_2905041913 - Original suggestion
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