bump(buildkite): 5bbd53d4 → a4bb20c6 (#5386)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

.claude-plugin/marketplace.json

@@ -643,7 +643,7 @@
       "source": {
         "source": "url",
         "url": "https://github.com/buildkite/skills.git",
-        "sha": "5bbd53d496b9dd5cd7b3e0a2d8345daa333c3f4e"
+        "sha": "a4bb20c6bf9ae535335f782015f65b9975065f27"
       },
       "homepage": "https://buildkite.com"
     },