Add gh vault plugin to allowed list (#154)

Author: ev1yehor

.buildkite/pull-requests.json

@@ -5,7 +5,7 @@
       "pipelineSlug": "logstash-filter-elastic-integration-pull-request",
       "allow_org_users": true,
       "allowed_repo_permissions": ["admin", "write"],
-      "allowed_list": ["dependabot[bot]", "mergify[bot]"],
+      "allowed_list": ["dependabot[bot]", "mergify[bot]", "elastic-vault-github-plugin-prod[bot]"],
       "set_commit_status": true,
       "build_on_commit": true,
       "trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:build|test)\\W+(?:this|it))",