Looks like a warning, but not a serious one. We don't use that package in NodeBB itself so it is likely one of its dependencies
Do you how to update a template like lavender ? I am a begginner with git.
assuming you aren't making any changes to the theme, you can just run
npm install nodebb-theme-vanilla(because lavender is based on vanilla)
npm install nodebb-theme-lavender
OR, if you want to update everything: