remove yarn stuff from the templates and ignore it (#2997)

We accidentally checked in yarn cache in the template folders. We shall
not do that.

### Change Type

- [x] `internal` — Any other changes that don't affect the published
package[^2]

templates/vite/.gitignore

@@ -1,2 +1,3 @@
 /*/node_modules
 node_modules
+.yarn/