Choose latest convex binary in evals (#811)

We guarantee that the version marked as `latest` will always have the
precompiled binary for all platforms. Thus, we should only use these and
not prerelease version.

Fixes a bug where a platform's binary could be missing.

Author: jordanhunt22

test-kitchen/convexBackend.ts

@@ -18,7 +18,7 @@ const admin_key =
 
 const convexRelease = fetch('https://api.github.com/repos/get-convex/convex-backend/releases')
   .then((r) => r.json())
-  .then((releases) => releases[0]);
+  .then((releases) => releases.find((release: any) => release.prerelease === false));
 
 const downloadBinaryMutex = new Mutex();
 const portMutex = new Mutex();