Fix typo in agent-proxy.md (elastic#2205)

Fix typo in substitution.

Author: vishaangelova

manage-data/ingest/ingest-reference-architectures/agent-proxy.md

@@ -29,7 +29,7 @@ Use when
 * Using [{{ls}} as proxy](ls-networkbridge.md) is not feasible.
 
 
-Currently {{agent}} is not able to present a certificate for connectivity to {{fleet-server}}. Therefore if a proxy placed between the {{agent}} and {{fleet-server}} is configured for mutual TLS, {{agents}} won’t be able to establish connectivity to {{fleet server}}.
+Currently {{agent}} is not able to present a certificate for connectivity to {{fleet-server}}. Therefore if a proxy placed between the {{agent}} and {{fleet-server}} is configured for mutual TLS, {{agents}} won’t be able to establish connectivity to {{fleet-server}}.
 
 
 ## Resources [agent-proxy-resources]