use @functools.lru_cache instead of @cache, for py 3.6 compat

inventory_provider/routes/msr.py

@@ -882,7 +882,8 @@ def get_peering_services():
     return Response(response, mimetype="application/json")
 
 
-@functools.cache
+# TODO: @functools.cache is only available in py3.9
+@functools.lru_cache
 def _load_all_interfaces():
     """
     loads all ip interfaces in the network and returns as a dict
@@ -909,7 +910,8 @@ def _load_all_interfaces():
     return result
 
 
-@functools.cache
+# TODO: @functools.cache is only available in py3.9
+@functools.lru_cache
 def _load_redundant_access_peers():
     """
     load all peers that should be considered