yanglint BUGFIX check of parent data node for oper

Checking that a parent data node exists in the datastore for the
nested-notification and action.
diff --git a/tools/lint/tests/data/modnotif_ds.xml b/tools/lint/tests/data/modnotif_ds.xml
new file mode 100644
index 0000000..efd835b
--- /dev/null
+++ b/tools/lint/tests/data/modnotif_ds.xml
@@ -0,0 +1 @@
+<con xmlns="urn:yanglint:modnotif"></con>