Allow null project id in service account module when reusing service account (#3452)

* allow null project id for service account reuse

* fix pf

tests/modules/iam_service_account/examples/reuse-0.yaml

@@ -0,0 +1,29 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+values:
+  module.service-account.google_billing_account_iam_member.billing-roles["ABCDE-12345-ABCDE-roles/billing.user"]:
+    billing_account_id: ABCDE-12345-ABCDE
+    condition: []
+    role: roles/billing.user
+  module.service-account.google_folder_iam_member.folder-roles["$folder_ids:test-roles/resourcemanager.folderAdmin"]:
+    condition: []
+    folder: folders/1234567890
+    role: roles/resourcemanager.folderAdmin
+
+counts:
+  google_billing_account_iam_member: 1
+  google_folder_iam_member: 1
+  modules: 1
+  resources: 2

tests/modules/project_factory/examples/example.yaml

@@ -620,7 +620,7 @@ counts:
   google_project_iam_member: 21
   google_project_service: 13
   google_project_service_identity: 4
-  google_service_account: 7
+  google_service_account: 6
   google_service_account_iam_binding: 1
   google_storage_bucket: 1
   google_storage_bucket_iam_binding: 2
@@ -630,5 +630,5 @@ counts:
   google_tags_tag_value: 2
   google_tags_tag_value_iam_binding: 1
   modules: 23
-  resources: 90
+  resources: 89
   terraform_data: 1