"Cachix setup coq" failed on CI

[andres-erbsen]

https://github.com/rocq-prover/stdlib/actions/runs/14823264339/job/41613093973?pr=136

  /home/runner/work/_actions/cachix/cachix-action/v15/dist/main/index.js:1702
                  error = new Error(`The process '${this.toolPath}' failed with exit code ${this.processExitCode}`);
                          ^
  
  Error: The process '/home/runner/.nix-profile/bin/cachix' failed with exit code 1
      at ExecState._setResult (/home/runner/work/_actions/cachix/cachix-action/v15/dist/main/index.js:1702:25)
      at ExecState.CheckComplete (/home/runner/work/_actions/cachix/cachix-action/v15/dist/main/index.js:1685:18)
      at ChildProcess.<anonymous> (/home/runner/work/_actions/cachix/cachix-action/v15/dist/main/index.js:1579:27)
      at ChildProcess.emit (node:events:524:28)
      at maybeClose (node:internal/child_process:1104:16)
      at ChildProcess._handle.onexit (node:internal/child_process:304:5)