rust: fix some warnings

6 jobs for master in 26 minutes and 45 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Check
passed #272614
check

00:00:22

 
  Test
passed #272615
flatpak

00:17:27

 
  Review
passed #272616
review

00:00:44

manual #272617
allowed to fail manual
stop_review
 
  Deploy
passed #272618
pages

00:08:11

passed pages:deploy

00:00:02