bug: keychain: updates break existing module

[octvs]

Are you following the right branch?

• My Nixpkgs and Home Manager versions are in sync

Is there an existing issue for this?

• I have searched the existing issues

Issue description

There are recent changes on keychain, including changes to the cli. This
new version has landed on unstable, and it is not complaint with the
existing module. For example it ignores the --agents option, which broke my
config. I was able to get around it via extraFlags, but the module needs an
update to mirror changes upstream.

If I can spare some time I will offer a PR, since I already had to read the
changes.

Maintainer CC

No response

System information

 - system: `"x86_64-linux"`
 - host os: `Linux 5.15.167.4-microsoft-standard-WSL2, NixOS, 25.05 (Warbler), 25.05.20250508.dda3dcd`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.28.3`
 - nixpkgs: `/nix/store/p893dkrzm5rxvhnqh092prgi1a7dzmcy-source`

[keysmashes]

for those not doing anything complicated and just wanting the warning about --agents to go away: if you only use Keychain for SSH (programs.keychain.agents = [ "ssh" ];), just remove that line.