chore(ci): skip autorelease workflow on non-release PRs (#756)

This PR was generated using Autosynth. 🌈

Synth log will be available here:
https://source.cloud.google.com/results/invocations/5ae39cfb-c9e2-4c0d-9bdc-85a69a45c240/targets

- [ ] To automatically regenerate this PR, check this box.

Source-Link: googleapis/synthtool@95dbe1b

.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:

synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquery.git",
-        "sha": "84d6632dbbdb9ccaf4afba545ec94a1156a989a2"
+        "sha": "03bda1bf79169bf0fca3ee12c1c3dfeb19c2e102"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "916c10e8581804df2b48a0f0457d848f3faa582e"
+        "sha": "95dbe1bee3c7f7e52ddb24a54c37080620e0d1a2"
       }
     }
   ],