build(java): enable snippet-bot (#305)

This PR was generated using Autosynth. 🌈

Synth log will be available here:
https://source.cloud.google.com/results/invocations/8e612041-fee6-48c6-a4b4-cd4a514d71be/targets

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

Source-Link: googleapis/synthtool@5a506ec

java-core/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-core.git",
-        "sha": "56f9d86d60228e72f56060262c3366a6220ee206"
+        "sha": "dcb6a6767d245ac134a1985c450c7ce5a2f2ee29"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "7c5370937dd9ba9dcf9cd7d2af880a58b389b4f1"
+        "sha": "5a506ec8765cc04f7e29f888b8e9b257d9a7ae11"
       }
     }
   ],
@@ -23,6 +23,7 @@
     ".github/PULL_REQUEST_TEMPLATE.md",
     ".github/readme/synth.py",
     ".github/release-please.yml",
+    ".github/snippet-bot.yml",
     ".github/trusted-contribution.yml",
     ".github/workflows/approve-readme.yaml",
     ".github/workflows/auto-release.yaml",