[Sprint/XerothermicXenarthra](chore): Change mature overlay text to NSFW #1279

Summary

Closes https://gitlab.com/minds/front/issues/1279

Changes the mature overlay text.

Steps to test

1. Flag a test account as NSFW from the admin account
2. Go to the test accounts channel
3. Overlay should be updated.

Estimated Regression Scope

Text only change.