fix: Shield ignores AuthToken::$authenticatorHeader config

[alxjzx100]

Description
Mentioned in discussion #1167
Fixes #1168

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[datamweb]

See :

#672 (comment)
https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/signing.md

[alxjzx100]

Signed, thank you.

[kenjis]

Please sign all your commits.

Also, we don't like merge commits. Please do not include merge commits in PRs if you can.
You can use git rebase to remove the merge commit.
See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/workflow.md#updating-your-branch

[datamweb]

LGTM!

[kenjis]

@alxjzx100 Thank you!