CI: Build appstream dependency

We need appstream >= 0.15.3 to get this fix:
  ximion/appstream#384

Without it the test-suite fails.

.github/workflows/check.yml

@@ -42,13 +42,23 @@ jobs:
  libfuse-dev ostree libostree-dev libarchive-dev libzstd-dev libcap-dev libattr1-dev libdw-dev libelf-dev python3-pyparsing \
  libjson-glib-dev shared-mime-info desktop-file-utils libpolkit-agent-1-dev libpolkit-gobject-1-dev \
  libseccomp-dev libsoup2.4-dev libcurl4-openssl-dev libsystemd-dev libxml2-utils libgpgme11-dev gobject-introspection \
- libgirepository1.0-dev libappstream-dev libdconf-dev clang socat meson libdbus-1-dev e2fslibs-dev bubblewrap xdg-dbus-proxy
+ libgirepository1.0-dev libappstream-dev libdconf-dev clang socat meson libdbus-1-dev e2fslibs-dev bubblewrap xdg-dbus-proxy \
+ python3-pip meson ninja-build libyaml-dev libstemmer-dev gperf itstool
  # One of the tests wants this
  sudo mkdir /tmp/flatpak-com.example.App-OwnedByRoot
  - name: Check out flatpak
  uses: actions/checkout@v1
  with:
  submodules: true
+ - name: Build appstream dependency # (We need at least 0.15.3 for the g_once fix)
+ run: |
+ sudo pip3 install 'meson~=0.62'
+ git clone --branch v0.15.4 --depth 1 --no-tags https://github.com/ximion/appstream.git ./appstream
+ pushd ./appstream
+ meson setup --prefix=/usr _build
+ ninja -C _build
+ sudo ninja -C _build install
+ popd
  - name: Create logs dir
  run: mkdir test-logs
  - name: autogen.sh