merge_variables: extend type detection failure message

Update the error message for the merge_variables lookup plugin in case an unsupported type is passed.

Author: rlenferink

changelogs/fragments/11107-extend-merge-variables-failure-message.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - merge_variables - extend type detection failure message to allow users for easier failure debugging (https://github.com/ansible-collections/community.general/pull/11107).

plugins/lookup/merge_variables.py

@@ -129,7 +129,7 @@ def _verify_and_get_type(variable):
     elif isinstance(variable, dict):
         return "dict"
     else:
-        raise AnsibleError("Not supported type detected, variable must be a list or a dict")
+        raise AnsibleError(f"Not supported type detected, variable must be a list or a dict: '{variable}'")
 
 
 class LookupModule(LookupBase):