Add next cache to clean command (#1811)

In our private repo we have a few next apps and they were not previously
being cleaned by the `yarn clean` command

### Change Type

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


### Release Notes

- Internal tooling change

scripts/clean.sh

@@ -27,6 +27,7 @@ goodbye .tsbuild
 goodbye .tsbuild-pub
 goodbye .tsbuild-dev
 goodbye .tsbuild-api
+goodbye .next
 
 rm -rf {packages,bublic/packages}/*/api
 rm -rf {packages,apps,bublic/packages,bublic/apps}/*/*.tgz