Silent types warnings of Host caches

Not worth writing the type here, we should better simplify this code and then
write types.

Author: philpep

testinfra/host.py

@@ -17,8 +17,8 @@
 
 
 class Host:
-    _host_cache = {}
-    _hosts_cache = {}
+    _host_cache = {}  # type: ignore[var-annotated]
+    _hosts_cache = {}  # type: ignore[var-annotated]
 
     def __init__(self, backend):
         self.backend = backend