Drop x86_64-darwin

Author: cole-h

.github/workflows/ci.yml

@@ -20,8 +20,6 @@ jobs:
         systems:
           - nix-system: "aarch64-darwin"
             runner: "macos-latest"
-          - nix-system: "x86_64-darwin"
-            runner: "macos-13"
           - nix-system: "aarch64-linux"
             runner: "namespace-profile-default-arm64"
           - nix-system: "x86_64-linux"