[8.18] (backport #18049) Stop waiting on ALL steps before staring junit annotation (#18054)

* Stop waiting on ALL steps before staring junit annotation (#18049)

The junit annotation previously would wait for EVERY step to finish before
running. It takes a non trivial amount of time and was consistenly adding
several minute to the total run time. The only artifacts it annotates are
emmited by the java unit tests. This commit updates the buildkite manifest to
properly define that relationship such that it will start as soon as the java
tests step is done instead of waiting for ALL steps.

(cherry picked from commit 91a9527)

# Conflicts:
#	.buildkite/pull_request_pipeline.yml

* Fix merge conflict

---------

Co-authored-by: Cas Donoghue <[email protected]>

Author: mergify[bot]

.buildkite/pull_request_pipeline.yml

@@ -337,10 +337,8 @@ steps:
       source .buildkite/scripts/common/container-agent.sh
       x-pack/ci/integration_tests.sh
 
-  - wait: ~
-    continue_on_failure: true
-
   - label: "🏁 Annotate JUnit results"
+    depends_on: "java-unit-tests"
     # the plugin requires docker run, hence the use of a VM
     agents:
       provider: gcp