ci(googlecas): fix QF1002 staticcheck — tagged switch on r.URL.Path

CI failure on commit a2a59a8 (run #423):

  internal/connector/issuer/googlecas/googlecas_failure_test.go:189:3:
    QF1002: could use tagged switch on r.URL.Path (staticcheck)

The OAuth2 token-refresh test handler had two cases — `r.URL.Path ==
"/token"` and `default` — both equality-against-r.URL.Path. Stati-
ccheck's QF1002 rule wants this expressed as a tagged switch:

  switch r.URL.Path {
  case "/token":
      ...
  default:
      ...
  }

The other four switches in the same file are mixed equality + Contains
(`case r.URL.Path == "/token":` + `case strings.Contains(r.URL.Path,
"/certificates"):`) — those are not tag-able and stay on
`switch { case ... }`. Only the OAuth2 test handler had the single-
equality-case pattern QF1002 fires on.

Test-only commit. No production code change.

Verified locally:
- gofmt clean.
- go test -short -count=1 ./internal/connector/issuer/googlecas/...
  green (5 failure tests + 14 happy-path subtests + 4 stub tests).

internal/connector/issuer/googlecas/googlecas_failure_test.go

@@ -186,8 +186,12 @@ func TestGoogleCAS_Issue_OAuth2TokenRefreshFailure_DistinguishedFromCAError(t *t
 	credPath := createTestCredentialsFile(t)
 
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		switch {
-		case r.URL.Path == "/token":
+		// Tagged switch on r.URL.Path keeps staticcheck QF1002 happy
+		// (only equality cases against a single field). The other
+		// failure tests use mixed equality + strings.Contains so they
+		// stay on `switch { case ... }`.
+		switch r.URL.Path {
+		case "/token":
 			w.Header().Set("Content-Type", "application/json")
 			w.WriteHeader(http.StatusUnauthorized)
 			_, _ = w.Write([]byte(`{"error":"invalid_grant","error_description":"Invalid JWT Signature."}`))