Fix Issue 20507 - Debug statements affect inference...

[MoonlightSentinel]

...of templated functions attributes.

This was caused by marking the function as @system/non-@nogc/non-nothrow BEFORE checking whether the statement is inside an debug statement / block

[dlang-bot]

Thanks for your pull request and interest in making D better, @MoonlightSentinel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20507	normal	Debug statements affect inference of templated functions attributes

Testing this PR locally

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

dub fetch digger
dub run digger -- build "master + dmd#10726"