Skip hostbased during Valgrind tests.

Valgrind doesn't let ssh exec ssh-keysign (because it's setuid) so skip
it during the Valgrind based tests.

See https://bugs.kde.org/show_bug.cgi?id=119404 for a discussion of this
(ironically there the problematic binary was ssh(1) back when it could
still be setuid).

.github/configs

@@ -166,8 +166,9 @@ case "$config" in
 	case "$config" in
 	    valgrind-1)
 		# All tests except agent-timeout (which is flaky under valgrind)
-		#) and slow ones that run separately to increase parallelism.
-		SKIP_LTESTS="agent-timeout ${tests2} ${tests3} ${tests4}"
+		# and hostbased (since valgrind won't let ssh exec keysign).
+		# Slow ones are run separately to increase parallelism.
+		SKIP_LTESTS="agent-timeout hostbased ${tests2} ${tests3} ${tests4}"
 		;;
 	    valgrind-2)
 		LTESTS="${tests2}"