simplify yml

Author: craff

.github/workflows/main.yml

@@ -11,8 +11,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-22.04, macos-latest]
-        arch: [x64, arm64]
+        os: [ubuntu-latest]
+        arch: [x64]
         ocaml-compiler:
           - "4.08"
           - "4.09"