`add-path` and `set-env` commands are disabled

[Utku Demir]

As of last week, add-path and set-env commands are disabled on GitHub actions, causing the nix-quick-install-action to fail. Here's an example build: https://github.com/utdemir/dotfiles/runs/1409013923

...
building '/nix/store/207knk81zf22gs5am710vn1x51s5gb3x-user-environment.drv'...
created 5 symlinks in user environment
Error: Unable to process command '::add-path::/home/runner/.nix-profile/bin' successfully.
Error: The `add-path` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
Error: Unable to process command '::set-env name=NIX_PROFILES::/nix/var/nix/profiles/default /home/runner/.nix-profile' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
Error: Unable to process command '::set-env name=NIX_USER_PROFILE_DIR::/nix/var/nix/profiles/per-user/runner' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
Error: Unable to process command '::set-env name=NIX_SSL_CERT_FILE::/etc/ssl/certs/ca-certificates.crt' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

The same issue was also present in cachix/install-nix-action and fixed by cachix/install-nix-action#52.

[Rickard Nilsson]

Thanks for bringing this to my attention! I've fixed the action and published release v4