ci: faster cargo check features

Bumping up the size of the runner, since we added more compute-intensive
logic back in [0]. The logic is still serialized, but now it should
complete faster. I've noticed the cache getting evicted faster lately,
due to multiple large PRs, so the extra compute will help offset the
delay caused by cache busting.

[0] f7234c0

.github/workflows/rust.yml

@@ -59,7 +59,7 @@ jobs:
 
   check:
     name: Check all crate features
-    runs-on: buildjet-8vcpu-ubuntu-2204
+    runs-on: buildjet-16vcpu-ubuntu-2204
     steps:
       - uses: actions/checkout@v4
         with: