Fix 20823 - un-@safe code fails with dip1000

[dkorpel]

It works now, simply add the test case

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20823	normal	[DIP 1000] un-@safe code fails with dip1000

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#14331"