[JamBalaya56562]

Closes: #4577
Closes: #4598

This takes over #4577 by @sundaypaulfz3-cell and #4598 by @rajveer002, which add the same kind of tests and have had no activity since 2026-09-18 and 2026-10-03 (#4577 is blocked on the Google CLA, and #4598 on the lint fix that @gmlewis asked for). Thank you both for the original work! If either of you would like to finish your PR instead, I'm happy to close this one.

GitHub App installation tokens now use the stateless ghs_APPID_JWT format, which is about 520 characters long instead of 40 (changelog). go-github already treats tokens as opaque strings, so this PR only adds tests that guard against length or format assumptions:

• TestAppsService_CreateInstallationTokenStateless checks that CreateInstallationToken returns such a token unchanged (from test: Cover stateless GitHub App token format #4598).
• TestClient_statelessInstallationToken checks that WithAuthToken sends it unchanged as Authorization: Bearer <token> (from test: Support stateless GitHub App installation tokens #4577).

Changes from #4577 and #4598:

• The test token follows the documented format: the ghs_ prefix, an app ID, and a JWT with two dots, 520 characters in total.
• Uses %v instead of %d for the fmtpercentv linter.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.64%. Comparing base (c678307) to head (3503f78).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4687   +/-   ##
=======================================
  Coverage   98.64%   98.64%           
=======================================
  Files         202      202           
  Lines       19004    19004           
=======================================
  Hits        18746    18746           
  Misses        258      258           

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[gmlewis]

Thank you, @JamBalaya56562!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @Not-Dhananjay-Mishra