Fix coverage on remote xdist nodes

scripts/Jenkinsfiles/python

@@ -27,6 +27,14 @@ def pythonTestCleanup() {
     bash scripts/xdist/terminate_xdist_nodes.sh'''
 }
 
+def xdist_git_branch() {
+    if (env.ghprbActualCommit) {
+        return "${ghprbActualCommit}"
+    } else {
+        return "${BRANCH_NAME}"
+    }
+}
+
 pipeline {
     agent { label "jenkins-worker" }
     options {
@@ -37,7 +45,7 @@ pipeline {
         XDIST_CONTAINER_SUBNET = credentials('XDIST_CONTAINER_SUBNET')
         XDIST_CONTAINER_SECURITY_GROUP = credentials('XDIST_CONTAINER_SECURITY_GROUP')
         XDIST_CONTAINER_TASK_NAME = "jenkins-worker-task"
-        XDIST_GIT_BRANCH = "${ghprbActualCommit}"
+        XDIST_GIT_BRANCH = xdist_git_branch()
     }
     stages {
         stage('Mark build as pending on Github') {