fix: Use BaseURL relative path for rate limit category

[auraseb]

bareDo passed req.URL.Path to GetRateLimitCategory, so on a client whose BaseURL has a path (GitHub Enterprise Server, /api/v3/) no prefix rule matched and search, code search, SCIM, source import, snapshot, SBOM and app manifest requests were all filed under CoreCategory. An exhausted code search limit then blocked unrelated core requests until it reset.

This strips the BaseURL path before categorizing. github.com clients are unaffected since their BaseURL path is /.

Tests:

• TestDo_rateLimitCategory_baseURLPath fails without the change: an exhausted search/code limit lands in rateLimits[CoreCategory] and blocks a following GET user.
• The existing search, SCIM, SBOM, snapshot, source import and app manifest tests used CoreCategory with the test server's /api-v3/ base path, which only worked because of this bug. They now pass their real category to testNewRequestAndDoFailureCategory.

Fixes #4643

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.62%. Comparing base (fef0352) to head (9dd7286).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4644   +/-   ##
=======================================
  Coverage   98.61%   98.62%           
=======================================
  Files         199      199           
  Lines       18694    18700    +6     
=======================================
+ Hits        18436    18442    +6     
  Misses        258      258           

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[gmlewis]

Thank you, @auraseb!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @Not-Dhananjay-Mishra