Fix issue 23333: Make DList range access @nogc

[AndrejMitrovic]

Unless I'm missing something this looked like an easy win to me.

Haven't done the full test-suite yet, and I am super out of date with what the newest dev/testing methodology is. Let me know if I've missed anything~

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23333	enhancement	DList range can be @nogc

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 + phobos#8567"

[AndrejMitrovic]

Should probably also test .back

[RazvanN7]

I'm not sure that this test is even required. I mean, if the code compiles with @nogc: that means that the functions that were annotated have passed compilation. I would simply drop this test.

[RazvanN7]

@AndrejMitrovic can you delete the test so that we can merge this?

[AndrejMitrovic]

@RazvanN7 done.