Don't block triggered JDK matrix Buildkite jobs (#15729) (#15731)

The recent PRs #15668 and #15705 refactored jobs with a custom schedule
to leverage a centralized trigger pipeline.

An unexpected sideffect of this is that the conditional for the wait
step doesn't work anymore.

This commit skips the wait step when the JDK matrix pipelines get triggered
from another pipeline.

(cherry picked from commit 82ac474b13)

Co-authored-by: Dimitrios Liappis <dimitrios.liappis@gmail.com>

.buildkite/linux_jdk_matrix_pipeline.yml

@@ -63,7 +63,7 @@ steps:
             value: "zulu_11"
 
   - wait: ~
-    if: build.source != "schedule"
+    if: build.source != "schedule" && build.source != "trigger_job"
 
   - command: |
       set -euo pipefail

.buildkite/windows_jdk_matrix_pipeline.yml

@@ -43,7 +43,7 @@ steps:
             value: "zulu_11"
 
   - wait: ~
-    if: build.source != "schedule"
+    if: build.source != "schedule" && build.source != "trigger_job"
 
   - command: |
       set -euo pipefail