ci: revert checkout ref change that broke pipeline

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: bluestreak01

ci/run_tests_pipeline.yaml

@@ -24,7 +24,6 @@ stages:
             fetchDepth: 1
             lfs: false
             submodules: false
-            ref: $(System.PullRequest.SourceBranch)
           - task: JavaToolInstaller@0
             displayName: "Install Java 11"
             inputs: