[4.0] Show debug bar on error page

[SharkyKZ]

Closes #29844.

Summary of Changes

Shows debug bar on error pages.

Testing Instructions

Enable debug.
Cause an error, e.g. a syntax error in templates/cassiopeia/index.php.

Actual result BEFORE applying this Pull Request

Debug bar not shown on error page.

Expected result AFTER applying this Pull Request

Debug bar shown on error page.

Documentation Changes Required

No.

[alikon]

I have tested this item ✅ successfully on ee05988

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[richard67]

I have tested this item ✅ successfully on ee05988

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[richard67]

RTC

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[wilsonge]

Thanks!