Fix naming convention for integration tests

Co-authored-by: Rye Biesemeyer <[email protected]>

Author: donoghuc

.buildkite/pull_request_pipeline.yml

@@ -219,7 +219,7 @@ steps:
       docker run -e FEDRAMP_HIGH_MODE=true test-runner-image ci/integration_tests.sh split  2 3
 
   - label: ":lab_coat: Integration Tests / part 1-of-3"
-    key: "integration-tests-part-1"
+    key: "integration-tests-part-1-of-3"
     agents:
       image: "docker.elastic.co/ci-agent-images/platform-ingest/buildkite-agent-logstash-ci-no-root"
       cpu: "8"