use pynxtools-xps main branch again

Author: lukaspie

.github/workflows/plugin_test.yaml

@@ -42,7 +42,7 @@ jobs:
             branch: main
             tests_to_run: tests/.
           - plugin: pynxtools-xps
-            branch: custom-attr-for-open-enum
+            branch: main
             tests_to_run: tests/.
           - plugin: pynxtools-xrd
             branch: main