build: fix cleanup of appimage: fix perms so rm -rf/git clean can work

copied this `  chmod -R 777 "${APP_DIR}"` from another place in the
build appimage script: cleanup worked ok locally in the end(after this line),
but not when paused early: so it seems it fixes the permissions and
we can put it in cleanup without sudo

Co-authored-by: Madman10K <[email protected]>

Author: alehander92

appimage-scripts/build_appimage.sh

@@ -12,6 +12,7 @@ set -e
 
 cleanup() {
   echo "Performing cleanup..."
+  chmod -R 777 "${APP_DIR}"
   rm -rf ./squashfs-root
 }