On error, just mark the error with `core.setFailed`, this is enough to
kill the process.

Replace child_process.execFileSync with '@actions/exec'.exec to be async
all the way.

clean error outputs

Avoid the following error when installing nix-unstable:

    experimental Nix feature 'nix-command' is disabled; use '--experimental-features nix-command' to override

only use stable nix commands

This allows filtering derivations to be pushed via an optional
`pushFilter` variable.

The use case behind it is to not push the actually built derivation, but
only runtime and build dependencies.

Signed-off-by: Sascha Grunert <mail@saschagrunert.de>

Add `pushFilter` to allow filtering cache derivations

Bumps [y18n](https://github.com/yargs/y18n) from 4.0.0 to 4.0.1.
- [Release notes](https://github.com/yargs/y18n/releases)
- [Changelog](https://github.com/yargs/y18n/blob/master/CHANGELOG.md)
- [Commits](https://github.com/yargs/y18n/commits)

Signed-off-by: dependabot[bot] <support@github.com>

chore(deps): bump y18n from 4.0.0 to 4.0.1

install-nix-action-v13

test nix master with cachix