Fix #8453 by making openssh listen on SSH_LISTEN_PORT not SSH_PORT (#8477)

docker/root/etc/s6/openssh/setup

@@ -26,6 +26,7 @@ fi
 
 if [ -d /etc/ssh ]; then
     SSH_PORT=${SSH_PORT:-"22"} \
+    SSH_LISTEN_PORT=${SSH_LISTEN_PORT:-"${SSH_PORT}"} \
     envsubst < /etc/templates/sshd_config > /etc/ssh/sshd_config
 
     chmod 0644 /etc/ssh/sshd_config

docker/root/etc/templates/sshd_config

@@ -1,4 +1,4 @@
-Port ${SSH_PORT}
+Port ${SSH_LISTEN_PORT}
 Protocol 2
 
 AddressFamily any
@@ -30,4 +30,4 @@ AllowUsers ${USER}
 Banner none
 Subsystem sftp /usr/lib/ssh/sftp-server
 
-AcceptEnv GIT_PROTOCOL
+AcceptEnv GIT_PROTOCOL