Update pull-requests.json (#3638)

Author: ev1yehor

.buildkite/pull-requests.json

@@ -30,7 +30,7 @@
         "pipeline_slug": "fleet-server-perf-tests",
         "allow_org_users": true,
         "allowed_repo_permissions": ["admin", "write"],
-        "allowed_list": ["mergify[bot]", "github-actions[bot]"],
+        "allowed_list": ["dependabot[bot]", "mergify[bot]", "github-actions[bot]"],
         "set_commit_status": false,
         "build_on_commit": false,
         "build_on_comment": true,