Add mod_builtin to special features so we can run the tests in CI

.github/workflows/rust.yml

@@ -251,7 +251,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        special_features: ["", "extensive_hints"]
+        special_features: ["", "extensive_hints", "mod_builtin"]
         target: [ test#1, test#2, test#3, test#4, test-no_std#1, test-no_std#2, test-no_std#3, test-no_std#4, test-wasm ]
     name: Run tests
     runs-on: ubuntu-22.04