Fix 22387 - Don't unconditionally override the type of an assert

[MoonlightSentinel]

The type might've already been set before, e.g. by defaultInitLiteral
for const(noreturn).init. Unconditionally setting the type to
noreturn would discard qualifiers and then cause problems in generic
code, e.g. for isBidirectionalRange!(const(noreturn)[]).

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22387	normal	Noreturn init loses type qualifiers

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#13168"