Revert "Disable broken macOS CI"

This reverts commit 8fc4cc4.

Author: sim642

.github/workflows/tests.yml

@@ -11,7 +11,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          # - macos-latest # TODO: fix
+          - macos-latest
           - ubuntu-latest
           # - windows-latest
         ocaml-version: