add test case for expired SSH certificate

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

sftpgo.json

@@ -16,7 +16,7 @@
     "kex_algorithms": [],
     "ciphers": [],
     "macs": [],
-    "trusted_user_ca_keys":[],
+    "trusted_user_ca_keys": [],
     "login_banner_file": "",
     "setstat_mode": 0,
     "enabled_ssh_commands": [
@@ -72,4 +72,4 @@
     "ca_certificates": [],
     "skip_tls_verify": false
   }
-}
+}