fix: auto_link() include trailing slashes

[corenominal]

Description
Fixes: #9165
Adjusted regular expression to include trailing slash.

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

[kenjis]

Thank you for sending this PR!

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• PRs must be sent to the appropriate branch
• All git commits must be GPG-signed
• Must follow our style guide
• Be commented in the PHP source file
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If pull requests do not comply with the above, they will likely be closed. Since we are a team of volunteers, we don't have any more time to work on the framework than you do. Please make it as painless for your contributions to be included as possible.

See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md

[kenjis]

1. Please sign all commits.
2. Add test code that proves the code works.
3. We do not use merge commits in PR branches. Please remove the merge commits. Use git rebase instead of git merge.

[github-actions]

👋 Hi, @corenominal!

We detected conflicts in your PR against the base branch 🙊
You may want to sync 🔄 your branch with upstream!

Ref: Syncing Your Branch

[kenjis]

Closed by #9169