Pin the accepted Google issuers with literals, not the module's own constant

While trimming that file under the cap I had rewritten the parametrize as
`[*lg._EXPECTED_ISSUERS]`, which asserts only that the module agrees with
itself: deleting a spelling from _EXPECTED_ISSUERS would have removed the case
that tests it and left the suite green.

Confirmed by mutation rather than by inspection -- dropping the bare
"accounts.google.com" from the module now fails
test_both_google_issuer_spellings_are_accepted[accounts.google.com], where
before it would have passed. Google uses both forms, so accepting both is a
real contract worth pinning.

432 passed, still 100%, verified with HOME redirected at a temp directory.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CFSGeWxHPY5rHUGrPqhcmG

crdt-sync/crdt_sync/tests/test_tool_link_google_token.py

@@ -49,7 +49,9 @@ def test_a_token_from_another_issuer_is_rejected() -> None:
         lg.describe_google_token(_google_token(iss="https://login.example.com"))
 
 
-@pytest.mark.parametrize("issuer", [*lg._EXPECTED_ISSUERS])
+@pytest.mark.parametrize(
+    "issuer", ["https://accounts.google.com", "accounts.google.com"]
+)
 def test_both_google_issuer_spellings_are_accepted(issuer: str) -> None:
     """Google uses both forms; rejecting either would be a false alarm."""
     assert "person@gmail.com" in lg.describe_google_token(_google_token(iss=issuer))