upstream: Expand $SSH to absolute path if it's not already.

Prevents problem later in increase_datafile_size if ssh is not in
the path.  Patch from quaresmajose via GHPR#510.

OpenBSD-Regress-ID: 2670a66af8b827410ca7139f0a89f4501cece77b

regress/test-exec.sh

@@ -1,4 +1,4 @@
-#	$OpenBSD: test-exec.sh,v 1.121 2024/10/22 07:13:28 dtucker Exp $
+#	$OpenBSD: test-exec.sh,v 1.122 2024/12/06 07:05:54 dtucker Exp $
 #	Placed in the Public Domain.
 
 #SUDO=sudo
@@ -184,6 +184,11 @@ case "$SSHD" in
 *) SSHD=`which $SSHD` ;;
 esac
 
+case "$SSH" in
+/*) ;;
+*) SSH=`which $SSH` ;;
+esac
+
 case "$SSHAGENT" in
 /*) ;;
 *) SSHAGENT=`which $SSHAGENT` ;;