ci(identity): run identity unit tests in the misc shard

tests/test_litellm/identity was not in any CI test-path, so the identity
unit tests never ran in CI and their coverage was never recorded. Codecov
therefore reported the identity source as uncovered even though the tests
exist and exercise it. Wire the dir into the misc shard so it runs and
reports coverage.

.github/workflows/test-unit-misc.yml

@@ -23,6 +23,7 @@ jobs:
     with:
       test-path: >-
         tests/test_litellm/secret_managers
+        tests/test_litellm/identity
         tests/test_litellm/a2a_protocol
         tests/test_litellm/anthropic_interface
         tests/test_litellm/completion_extras