chore(ci): remove unused macOS gc config

Author: ryoppippi

.github/actions/setup-nix/action.yaml

@@ -23,7 +23,6 @@ runs:
           nix-${{ runner.os }}-${{ hashFiles('flake.lock') }}-
           nix-${{ runner.os }}-
         gc-max-store-size-linux: 1G
-        gc-max-store-size-macos: 1G
 
     - name: Install tools from nixpkgs
       shell: bash