[trivial] fix issue 19730 - if (auto x) {} isn't properly rejected

[ghost]

To match the rule

 TypeCtors Identifier = Expression

even if accepting the invalid code didn't hurt.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19730	regression	if (auto x) {} isn't properly rejected

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 "stable + dmd#9447"

[thewilsonator]

Otherwise Looks good

[Geod24]

Please add tests for if (const size_t value) as well.
Buildkite seems to indicate this would break with this PR

[ghost]

Yeah this "trivial" PR is a failure right now and it's very surprising not to see the form of IfCondition that it breaks in the whole official test suite.