Update settings.json

[rodinux]

resolve an issue since v1.9.1

Problem

• ran into the malformed color: false problem, and it appears to be caused by using a settings.json file from a pre-v1.9.0 version.

Solution

• change the values by null for the options name an color seems fix that after read this https://github.com/ether/etherpad-lite/issues/5799#issuecomment-1616186527

PR Status

• [ ] Code finished and ready to be reviewed/tested
• [ ] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[rodinux]

I have tested, it seems fix this issue.