macos: always pass -a "${VOLUME}" and -s "Nix Store"

[hispirus]

Description

/usr/bin/security {add,find,delete}-generic-password accepts both -a account and -s service parameters as password lookup keys. Always pass -a "${VOLUME}" and -s "Nix Store". With this change, installation succeeds even with --encrypt set to true and --volume-label set to any value deviating from Nix Store.

Checklist

• Formatted with cargo fmt
• Built with nix build
• Ran flake checks with nix flake check
• Added or updated relevant tests (leave unchecked if not applicable)
• Added or updated relevant documentation (leave unchecked if not applicable)
• Linked to related issues (leave unchecked if not applicable)

Validating with install.determinate.systems

If a maintainer has added the upload to s3 label to this PR, it will become available for installation via install.determinate.systems:

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix/pr/$PR_NUMBER | sh -s -- install

[cole-h]

Thanks, @hispirus! Sorry for the huge delay in reviewing your PR. It all looks good to me!

I opened a new PR (#1418) with your changes because I couldn't push a small followup change (using a constant for the Nix Store service string) here since you had maintainer edits disabled.