build(nodejs): make default_version optional (#1368)

Source-Link: googleapis/synthtool@1f06210
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:8730ec2b4f2a998e81626bcb2acf001f5148ef5d2e1ab7de38c3055444dc0bee

.github/.OwlBot.lock.yaml

@@ -1,3 +1,16 @@
+# Copyright 2022 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.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest
-  digest: sha256:2d850512335d7adca3a4b08e02f8e63192978aea88c042dacb3e382aa996ae7c
+  digest: sha256:8730ec2b4f2a998e81626bcb2acf001f5148ef5d2e1ab7de38c3055444dc0bee