tab: Free the shader in unrealize() instead of dispose()

4 jobs for wip/exalm/shader-crash in 5 minutes and 45 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Build
passed abi-check #1399340

00:01:34

passed api-visibility #1399337

00:00:11

passed build-flatpak #1399339
flatpak

00:05:44

passed doc #1399338
flatpak

00:01:46