ci: Add ABI check

Last ABI break was when we fixed the return value for fp_get_pollfds()
in commit 056ea541.
2 jobs for wip/hadess/add-abi-check in 3 minutes and 18 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Build
passed #473168
build

00:01:38

 
  Test
passed #473169
flatpak master

00:01:40