Fix bcupgrade group name

Author: breskeby

.buildkite/scripts/run-pr-upgrade-tests.sh

@@ -26,7 +26,7 @@ echo "Running PR upgrade tests from $BUILDKITE_PULL_REQUEST_BASE_BRANCH [$BASE_C
 
 cat << EOF | buildkite-agent pipeline upload
 steps:
-    - group: "pr-upgrade $BC_BUILD_ID -> $BUILDKITE_BRANCH"
+    - group: "pr-upgrade $BUILDKITE_PULL_REQUEST_BASE_BRANCH -> $BUILDKITE_BRANCH"
       steps:
         - label: "pr-upgrade-part-{{matrix.PART}}"
           command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true -Dorg.elasticsearch.build.cache.push=true -Dignore.tests.seed -Dscan.capture-file-fingerprints -Dtests.bwc.main.version=${VERSION}-SNAPSHOT -Dtests.bwc.refspec.main=${BASE_COMMIT} bcUpgradeTestPart{{matrix.PART}} -Dtests.jvm.argline="-Des.serverless_transport=true"