upstream: Fix typo. From AlexanderStohr via github PR#343.

OpenBSD-Commit-ID: a134c9b4039e48803fc6a87f955b0f4a03181497

Author: daztucker

PROTOCOL.agent

@@ -54,7 +54,7 @@ Where a constraint consists of:
 	string		to_hostname
 	keyspec[]	to_hostkeys
 
-An a keyspec consists of:
+And a keyspec consists of:
 
 	string		keyblob
 	bool		is_ca
@@ -81,4 +81,4 @@ the constraint is:
 
 This option is only valid for XMSS keys.
 
-$OpenBSD: PROTOCOL.agent,v 1.17 2022/05/09 08:25:27 dtucker Exp $
+$OpenBSD: PROTOCOL.agent,v 1.18 2022/09/21 22:26:50 dtucker Exp $