chore: increase circleci test job size to 2xlarge

It was failing with:

   Compiling ethportal-peertest v0.1.0 (/home/circleci/project/ethportal-peertest)
error: linking with `cc` failed: exit status: 1
...<snip>...
  = note: collect2: fatal error: ld terminated with signal 9 [Killed]
          compilation terminated.

This looks a lot like an OOM killer. It's not the first time that it's
happened, so maybe increasing the box size will help.

Author: carver

.circleci/config.yml

@@ -162,7 +162,7 @@ jobs:
   test:
     description: |
       Run tests.
-    resource_class: xlarge
+    resource_class: 2xlarge
     executor:
       name: rust/default
       tag: 1.71.1