[stable] Fix typo in dmd.expression apparently causing sporadic frontend crashes

[kinke]

Cherry-pick of #8294 for stable; sorry for targeting the wrong branch.

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[WalterBright]

I think stable will need #8249 as the boot compiler was upgraded.

[wilzbach]

I think stable will need #8249 as the boot compiler was upgraded.

-> #8314

[wilzbach]

Stable should be green again now.