Forbid using HANDY_USE_UNSTABLE_API

To help applications know they should stop using HANDY_USE_UNSTABLE_API,
error out if it is defined.
11 jobs for forbid-unstable-api in 15 minutes and 1 second (queued for 1 second)
latest
Status Name Job ID Coverage
  Build
passed api-visibility #845798

00:00:24

passed build-debian-clang #845800

00:06:49

passed build-debian-gcc #845799

00:01:56

passed build-fedora-gcc #845801

00:06:42

passed build-flatpak #845802
flatpak

00:01:15

passed build-flatpak-glade #845803
flatpak

00:03:19

 
  Test+Docs
passed build-gtkdoc #845804

00:02:15

passed unit-test #845805

00:02:18

44.1%
 
  Package
passed package-debian-buster #845806

00:03:10

 
  Test Package
passed autopkgtest-debian-buster-package #845807

00:02:41

passed lintian-debian-buster-package #845808

00:01:15