fix(testing): Fix fake provider reverting strings with emojis

[nickvergessen]

Before	After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[ChristophWurst]

👍

[nickvergessen]

Fixed only cs+rector:

[40](https://github.com/nextcloud/server/actions/runs/24246433101/job/70793882121?pr=59566#step:5:141)
-		for ($i = mb_strlen($str); $i>=0; $i--) {
+		for ($i = mb_strlen($str); $i >= 0; $i--) {

[nickvergessen]

/backport to stable33