fix: anchors in readme

[Zarthus]

Fixes the "Checkout multiple repos (private)" anchors in the README

They were previously not doing anything, now when you click on it it directs you to the right location

• https://github.com/actions/checkout#Checkout-multiple-repos-private (brings you nowhere)
• https://github.com/actions/checkout#checkout-multiple-repos-private (fixed)

You can view the rendered view of the README on my fork: https://github.com/Zarthus/checkout/tree/fix/readme-anchors

[pfeerick]

There's more... 🤭 I just ran into this one...
https://github.com/actions/checkout#checkout-pull-request-head-commit-instead-of-merge-commit

[Zarthus]

Thanks! Makes me wonder if it's an intentional thing to support another tool (i.e. some documentation generation tool)

[pfeerick]

Maybe it's just sanitised to all lower case? 🤷

[FlorianCassayre]

Thanks, I noticed this too. We should push this fix forward because it can be confusing.