chore(ci): skip autorelease workflow on non-release PRs (#156)

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Synth log will be available here:
https://source.cloud.google.com/results/invocations/cb8e9e40-1c94-4237-af69-70f70fdb6d3a/targets

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Source-Link: googleapis/synthtool@95dbe1b

java-shared-dependencies/.github/workflows/auto-release.yaml

@@ -4,6 +4,7 @@ name: auto-release
 jobs:
   approve:
     runs-on: ubuntu-latest
+    if: contains(github.head_ref, 'release-v')
     steps:
     - uses: actions/github-script@v3.0.0
       with:

java-shared-dependencies/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-shared-dependencies.git",
-        "sha": "3252f47271e04e3fcd520ac15ffdfa06cb2dda03"
+        "sha": "79946122e194c67eac609e42ef73917c59c12daa"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "916c10e8581804df2b48a0f0457d848f3faa582e"
+        "sha": "95dbe1bee3c7f7e52ddb24a54c37080620e0d1a2"
       }
     }
   ],