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>

www/css/ext6-pbs.css

@@ -224,3 +224,9 @@ p.logs {
 .x-action-col-icon.critical:before {
     color: #FF6C59;
 }
+
+.pve-icon-verify-lettering:after {
+    color: #464d4d;
+    font-weight: bold;
+    content: "V.";
+}