gce: don't ICE on non-local const Fixes rust-lang/rust#133808 I have absolutely no idea what I'm doing here, but I followed `@BoxyUwU` 's [instructions](https://github.com/rust-lang/rust/issues/133808#issuecomment-3009122957), and turns out this small change fixes rust-lang/rust#133808, and doesn't seem to break anything else. (This code path is only reachable when the GCE feature gate is enabled, so even if it does break in a way that is not caught by current test coverage, I guess it's not as bad as breaking stable or non-incomplete features?) Anyways, r? `@BoxyUwU` , if you don't mind.