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

(cherry picked from commit 66ffce7)

Author: bluca

.github/workflows/mkosi.yml

@@ -74,6 +74,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9
+
+    - name: Build dependencies
+      run: sudo apt install --yes makepkg
+
     - uses: systemd/mkosi@5866c0ff3b36d350c943016e5a3b115f7a95d37f
 
     - name: Configure