audio-video-properties: Make the framerate more precise

Add a bit more precision to the frames per second property.

Closes: #901
3 jobs for master in 8 minutes and 3 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #214144
flatpak devel

00:06:56

9.1%
 
  Deploy
passed #214145
pages

00:01:07

passed pages:deploy

00:00:00