Install xeus-python for the js-debugger job

scripts/ci_install.sh

@@ -35,3 +35,8 @@ if [[ $GROUP == nonode ]]; then
     sudo rm -rf $(which node)
     ! node
 fi
+
+# The debugger tests require a kernel that supports debugging
+if [[ $GROUP == js-debugger ]]; then
+    pip install xeus-python>=0.8
+fi