nix: upgrade Nix 2.3.6 to 2.3.12
nix: upgrade Nix 2.3.6 to 2.3.12

This should also fix issues with MacOS sandboxing:
```
sandbox-exec: execvp() of '/nix/store/...-bash-4.4-p23/bin/bash' failed: Operation not permitted
```
https://github.com/cachix/install-nix-action/issues/15

Signed-off-by: Jakub Sokołowski <1d3764b91b902f6b45836e2498da81fe35caf6d6@status.im>

status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react