chore: add aur makepkg build test script

and did you know that makepkg updates stuff like the -git pkg version? :o

assets/pkg/aur/test-makepkg.sh

@@ -0,0 +1,15 @@
+#/usr/bin/env bash
+set -e
+
+MYSELF=$(realpath "$0")
+MYDIR=$(dirname "$MYSELF")
+
+for pkg in "$MYDIR"/*/; do
+    cd "$pkg"
+    printf "\x1b[1mEntering '%s'\x1b[0m\n" "$pkg"
+
+    rm -rf *.{gz,zst} src pkg
+    makepkg -f .
+
+    echo
+done