fix(server): regular version check (#7620)

`dt.diffNow()` equals `dt.diff(DateTime.now())`, so it returns a
negative number when `dt` is in the past (which it always is in this
case).

Therefore we could only get over the condition during startup (when
`this.releaseVersionCheckedAt` isn't set yet), effectively breaking
update notifications while the server is running.

server/src/domain/server-info/server-info.service.ts

@@ -149,7 +149,7 @@ export class ServerInfoService {
       }
 
       // check once per hour (max)
-      if (this.releaseVersionCheckedAt && this.releaseVersionCheckedAt.diffNow().as('minutes') < 60) {
+      if (this.releaseVersionCheckedAt && DateTime.now().diff(this.releaseVersionCheckedAt).as('minutes') < 60) {
         return true;
       }