📚 branch-protection.md :: `required_linear_history` vs. `require_linear_history`

## Problem Description
The docs show miss-match spelling for property.
https://github.com/github/safe-settings/blob/main-enterprise/docs/github-settings/5.%20branch-protection.md

### What is actually happening

Based on the code search I see that [`required_linear_history`](https://github.com/search?q=repo%3Agithub%2Fsafe-settings%20required_linear_history&type=code) looks to be the valid spelling.

### What is the expected behavior

Docs should show correct property spelling.