Fix issue 19456 - ParameterIdentifierTuple incorrect for abstract met…

[Biotronic]

…hods with unnamed parameters

[dlang-bot]

Thanks for your pull request and interest in making D better, @Biotronic! 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
✓	19456	normal	ParameterIdentifierTuple incorrect for abstract methods with unnamed parameters

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 + phobos#6789"