Separator for table direct children @5.1.2

[PerseusTheGreat]

Prerequisites

• I have searched for duplicate or closed issues
• I have validated any HTML to avoid common problems
• I have read the contributing guidelines

Describe the issue

Hi.
After updating to 5.1.2, in tables that have <colgroup> before <thead>, a border appears above <thead>.
I think the new added rule (#34861) needs to be extended.

Reduced test cases

Current situation:
https://codepen.io/laylazi/pen/MWvWjaM

My proposal:
https://codepen.io/laylazi/pen/dyzypQd

What operating system(s) are you seeing the problem on?

Windows

What browser(s) are you seeing the problem on?

Chrome, Firefox, Microsoft Edge

What version of Bootstrap are you using?

5.1.2

[danielmatthew]

If a <caption> is included too, this causes the <thead>'s top border to render, as .table>:not(:first-child) matches.

See reproduction: https://codepen.io/danielmatthew/pen/zYdROzJ

[ffoodd]

Yup, that's covered by the latest linked PR.

[mbrodala]

Since the link is very easy to miss: #35200

[mdo]

Resolved through #35908.