GHA: install makepkg manually

/usr/bin/pacman-key: line 31: /usr/share/makepkg/util/message.sh: No such file or directory
/usr/bin/pacman-key: line 32: /usr/share/makepkg/util/parseopts.sh: No such file or directory
/usr/bin/pacman-key: line 620: parseopts: command not found

Author: bluca

.github/workflows/mkosi.yml

@@ -74,6 +74,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
+
+    - name: Build dependencies
+      run: apt install --yes makepkg
+
     - uses: systemd/mkosi@bbe715f42911f9660712377a5b39335b9391ae22
 
     - name: Configure