Xorfor

### Prerequisites - [X] I have [searched](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue) for duplicate or closed feature requests - [X] I have read the [contributing guidelines](https://github.com/twbs/bootstrap/blob/main/.github/CONTRIBUTING.md) ### Proposal Currently the class `table-group-divider` adds a thicker...