Fix in dict_merge to check for Mapping

*  Based on review comments for PR #49474 change the check
   for isinstance from `dict` to `Mapping`

lib/ansible/module_utils/network/common/utils.py

@@ -37,6 +37,7 @@ from itertools import chain
 from socket import inet_aton
 
 from ansible.module_utils._text import to_text
+from ansible.module_utils.common._collections_compat import Mapping
 from ansible.module_utils.six import iteritems, string_types
 from ansible.module_utils.basic import AnsibleFallbackNotFound
 
@@ -301,7 +302,7 @@ def dict_merge(base, other):
             if key in other:
                 item = other.get(key)
                 if item is not None:
-                    if isinstance(other[key], dict):
+                    if isinstance(other[key], Mapping):
                         combined[key] = dict_merge(value, other[key])
                     else:
                         combined[key] = other[key]