flatpak: Pass GDK_ env vars when running a command in the sandbox

4 jobs from master in 69 minutes and 41 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Docker Image
passed #90510
pitivi:1.0

00:49:04

passed #90509
pitivi:master

00:59:34

 
  Build
passed #90511
build

00:06:58

 
  Test Results
passed #90512
test-results

00:03:08