Use separate versions.tofu for OpenTofu constraints

modules/certificate-manager/versions.tofu

@@ -0,0 +1,29 @@
+# Copyright 2024 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
+#
+#     https://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.
+
+# Fabric release: v36.0.1
+
+terraform {
+  required_version = ">= 1.8.0"
+  required_providers {
+    google = {
+      source  = "hashicorp/google"
+      version = ">= 6.13.0, < 7.0.0" # tftest
+    }
+    google-beta = {
+      source  = "hashicorp/google-beta"
+      version = ">= 6.13.0, < 7.0.0" # tftest
+    }
+  }
+}