Fix 21668 - Cannot declare ref parameter of opaque type

[MoonlightSentinel]

Don't raise errors for VarDeclarations that are marked as ref

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21668	minor	Cannot declare ref parameter of opaque type

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 "stable + dmd#12239"