cloudapi: update expected image type test for gcp-rhui

gce-rhui is now gone from RHEL 9 [1] and the old name simply aliases to
gce.  gcp-rhui in the cloudapi now resolves to 'gce' in RHEL 9 and
'gce-rhui' in RHEL 8.

[1] osbuild/images#857

internal/cloudapi/v2/compose_test.go

@@ -674,7 +674,13 @@ func TestGetImageRequests_ImageTypeConversion(t *testing.T) {
 		},
 		{
 			requestedImageType: ImageTypesGcpRhui,
-			requestedDistros:   []string{rhel8, rhel9},
+			requestedDistros:   []string{rhel9},
+			expectedImageType:  "gce",
+			expectedTargetName: target.TargetNameGCP,
+		},
+		{
+			requestedImageType: ImageTypesGcpRhui,
+			requestedDistros:   []string{rhel8},
 			expectedImageType:  "gce-rhui",
 			expectedTargetName: target.TargetNameGCP,
 		},