Fix Issue 23306 - @disable new() ought not disable scope A = new A

[RazvanN7]

I only added this check for class declarations because, although allowed by the compiler, scope struct declarations that are allocated with new seem nonsensical.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23306	enhancement	@disable new() ought not disable `scope A = new A`

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#14403"