add pull request source branch to TC trigger call

Author: bigorn0

.github/workflows/trigger-pr-tests-plugins.yml

@@ -15,5 +15,5 @@ jobs:
             -X POST \
             -H 'Authorization: Bearer ${{ secrets.TEAMCITY_TRIGGER_TESTS_TOKEN }}' \
             -H 'Content-Type: application/json' \
-            -d '{"branchName": "pull/${{ github.event.number }}", "buildType": {"id": "${{ vars.TEAMCITY_BUILD_ID_FOR_TESTING_PLUGIN_PR }}"}}' \
-            ${{ vars.TEAMCITY_API_URL }}/buildQueue
+            -d '{"branchName": "pull/${{ github.event.number }}", "sourceBranch": "${{ github.event.pull_request.head.ref }}", "buildType": {"id": "${{ vars.TEAMCITY_BUILD_ID_FOR_TESTING_PLUGIN_PR }}"}}' \
+            ${{ vars.TEAMCITY_API_URL }}/buildQueue