[BUGFIX] Explicitly use control characters in HTML fixture

`RenderPreviewImportPageAndRecordsByUpdateWithDiff.php` has HTML markup
with line breaks and tab characters. With some IDEs this may break if
lines containing a tab only will get trimmed. All such characters are
now replaced by explicit control characters to make sure the expectation
does not break anymore when saving this file.

Resolves: #97300
Releases: main, 11.5
Change-Id: Ifc5d7e39d6d69176b111d3361f741a89866f008b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74142


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>