MDEV-31216: Make sure that lsof does not fail on install

Command lsof can fail on Debian install.
Revert logic more like old one to make sure that there is no failing
and still does don't boundce on shellcheck.

debian/mariadb-server-10.6.postinst

@@ -125,10 +125,10 @@ EOF
     # This direct update is needed to enable an authentication mechanism to
     # perform mariadb-upgrade, (MDEV-22678).  To keep the impact minimal, we
     # skip innodb and set key-buffer-size to 0 as it isn't reused.
-    lsof -nt "$mysql_datadir"/mysql/user.MYD > /dev/null
-    lsof_rtn_code=$?
-    if [ -f "$mysql_datadir/auto.cnf" ] && [ -f "$mysql_datadir/mysql/user.MYD" ] &&
-    [ ! ${lsof_rtn_code} ] && [ ! -f "$mysql_datadir/undo_001" ]
+    if [ -f "$mysql_datadir/auto.cnf" ] &&
+    [ -f "$mysql_datadir/mysql/user.MYD" ] &&
+    ! lsof -nt "$mysql_datadir"/mysql/user.MYD > /dev/null &&
+    [ ! -f "$mysql_datadir/undo_001" ]
     then
       echo "UPDATE mysql.user SET plugin='unix_socket' WHERE plugin='auth_socket';" |
       mariadbd --skip-innodb --key_buffer_size=0  --default-storage-engine=MyISAM --bootstrap 2> /dev/null