List widget form input prevents whitespace and commas

**Describe the bug**
When trying to write in list widget input field a comma separated list, it is impossible to add whitespaces or comma.
This was introduced with `v2.10.65`

**To Reproduce**
1. Add a list widget to any collection fields through config
```
- name: tags
label: Tags
widget: list
```
2. Go to CMS dashboard and try and edit the field (using whitespace, commas, tabs etc...)

**Expected behavior**
The user should be able to write in commas and whitespace in the form field.

**Applicable Versions:**
- Netlify CMS version: 2.10.65 and above
- Git provider: GitBhug
- OS: MacOS Catalina 10.15.7
- Browser version: Chrome Version 86.0.4240.198

**CMS configuration**
https://tnd-modules.netlify.app/cms/config.html

Start by reproducing the issue with the provided list widget configuration in the CMS dashboard, testing spaces, commas, and tabs in the input. Done means list widget users can enter whitespace and commas, including on the affected Netlify CMS versions.

Written by the indexing model from the issue text.