ui: datastore: use simple V. for verify action button

ui: datastore: use simple V. for verify action button

Choosing a good icon is hard here, while the magnifying glass is
somewhat relatable, it reminds to much of a "Search" function, which
can be quite confusing here.

So use a simple "V.", even if it's probably also not to ideal..

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>