Changes to style files are not picked up by `assets watch`

Package version (if known): 1.0.11

## Describe the bug

While `invenio-cli assets watch` is up, changes in your instance's assets/ folder are not picked up (no rebuild is triggered).

## Steps to Reproduce

Cookie cutter an instance of InvenioRDM and follow the official instructions to bring it up locally (install, setup, run) while on another shell bring up `invenio-cli assets watch`.

Make any changes to the files shipped by default under assets/less/site/globals (e.g. to `site.variables`, as suggested by the official instructions). A rebuild is required to see any changes (i.e. `invenio-cli assets build`) which may not be desirable, considering the time it takes.

## Expected behavior

Changes to the mentioned files are expected to trigger a (hot) reload of the webpack build.

## Workaround

As suggested by @kpsherva , this works:

`ln -s /assets/less/cds-rdm ~/.virtualenvs//var/instance/assets/less`

But it must be done every time a full rebuild happens (i.e. on `invenio-cli assets build`). The `VIRTUALENV` path can be seen for example when running `pipenv shell` and checking where it's activated from.