GHA: Add meson install step

.github/workflows/unit_tests.yml

@@ -11,18 +11,25 @@ jobs:
   build:
     runs-on: ubuntu-22.04
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python 3.10
-      uses: actions/setup-python@v2
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.8
+      uses: actions/setup-python@v5
       with:
-        python-version: "3.10"
+        python-version: "3.8"
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
         sudo apt-get update
-        sudo apt install -y libgirepository1.0-dev gir1.2-gtk-4.0 libgtksourceview-5-dev
+        sudo apt install -y meson gettext itstool libgirepository1.0-dev gir1.2-gtk-4.0 libgtksourceview-5-dev
         pip install --user -e git+https://github.com/getting-things-gnome/liblarch.git#egg=liblarch
         pip install --user pytest pycairo PyGObject caldav lxml
+    - name: Build and install GTG
+      run: |
+        meson setup --prefix=${PWD}/inst ./build
+        cd build
+        meson compile
+        sudo meson install
     - name: Run unit tests with Pytest
       run: |
-        ./run-tests
+        export PYTHONPATH=${PWD}/inst/lib/python3.8/site-packages
+        pytest