export.sh: keep build/ out of the game (a .gdignore): screenshots and voice samples there were being packed into it

tools/export.sh

@@ -25,6 +25,10 @@ for v in $(grep -E '^application/(short_version|version|file_version|product_ver
 done
 which=${1:-all}
 mkdir -p build
+# Godot mustn't import build/ (screenshots, samples, the site): with
+# all_resources, anything it imported there went into the game too.
+touch build/.gdignore
+find build -name "*.import" -delete
 "$GODOT" --headless --path . --import >/dev/null 2>&1
 
 if [ "$which" = all ] || [ "$which" = macOS ]; then