Disable format-version-forward-back test on el9+.

Using t_skip, we just skip this test on el9.

If we ever want to add a formatversion 2->3 test, perhaps we should
just add a separate test script, instead of going over a static array.

But let's not worry about this too much right now.

Signed-off-by: Auke Kok <auke.kok@versity.com>

tests/tests/format-version-forward-back.sh

@@ -11,6 +11,11 @@
 # format version.
 #
 
+# not supported on el9!
+if [ $(source /etc/os-release ; echo ${VERSION_ID:0:1}) -gt 8 ]; then
+	t_skip "Unsupported OS version"
+fi
+
 mount_has_format_version()
 {
 	local mnt="$1"