bk: update junit-annotate to run faster (#5540)

Author: Copilot

.buildkite/pipeline.yml

@@ -225,11 +225,13 @@ steps:
             limit: 1
 
       - label: ":junit: Junit annotate"
+        agents:
+          # requires at least "bash", "curl" and "git"
+          image: "docker.elastic.co/ci-agent-images/buildkite-junit-annotate:1.0"
         plugins:
-          - junit-annotate#v2.4.1:
+          - junit-annotate#v2.7.0:
               artifacts: "build/*.xml"
-        agents:
-          provider: "gcp"
+              run-in-docker: false
         depends_on:
           - step: "unit-test"
             allow_failure: true