add flatpak nightly manifest

2 jobs for !67 with flatpak in 18 minutes and 38 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #23119
build_ubuntu_18_04

00:07:38

passed #23118
linux kf5-qt5 qt5.12

00:18:38

42.0%