tpl/collections: Include key in IsSet unsupported-type warning

The warning logged when calling IsSet with an unsupported type did not
identify which key triggered it, making it hard to locate the offending
template. Include the key in the message.

Fixes #11794

tpl/collections/collections.go

@@ -347,7 +347,7 @@ func (ns *Namespace) IsSet(c any, key any) (bool, error) {
 			return av.MapIndex(kv).IsValid(), nil
 		}
 	default:
-		ns.deps.Log.Warnf("calling IsSet with unsupported type %q (%T) will always return false.\n", av.Kind(), c)
+		ns.deps.Log.Warnf("calling IsSet with unsupported type %q (%T) for key %v will always return false.\n", av.Kind(), c, key)
 	}
 
 	return false, nil