Error when pushing using personal access token -- the requested URL returned error: 403

Context:
Was checking out multiple private repos and was copying a file from a private repos to a public repos in the workspace, then committing and pushing. The push would fail with a 403.

Error:
```
remote: Permission to my-repos denied to github-actions[bot].
fatal: unable to access 'https://github.com/.../my-repos.git/': The requested URL returned error: 403
```

By running this command we can see any of config settings being used for our repos:
```
git config -l
```

We discovered the checkout action is executing a command like this:
```
git config --local http.https://github.com/.extraheader AUTHORIZATION: basic ***
```
Reference:
https://github.com/actions/checkout/blob/master/adrs/0153-checkout-v2.md#pat

The fix is to do this:
```
git config --local --unset-all "http.https://github.com/.extraheader"
```

It's seems unlikely that this could lead to side effects but it may be desirable to re-set this value after the push is completed.

Sorry for lack of PR, we ended up not using your action and just incorporated what we ended into our workflow file.