incorrect sql example in manual cluster upgrade doc

[aliher1911]

Current docs:

SET CLUSTER SETTING cluster.preserve_downgrade_option = 'v22.2';

but it should be

SET CLUSTER SETTING cluster.preserve_downgrade_option = '22.2';

instead.

Location:

https://github.com/cockroachdb/docs/blob/master/v23.1/upgrade-cockroach-version.md?plain=1#L124

Must be trivial fix, but I'm not familiar with syntax of template.