#1071 fix: resolve fish test path correctly with fishtape

The issue was that (status dirname) returns unexpected values when fish test files are run via fishtape in CI. This caused the path resolution to fail, resulting in 'Unknown command' errors.

Fix: Use relative path ../../home-manager/programs/fish/functions directly instead of relying on status dirname, since fishtape runs with the test file's directory as the current working directory.

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Summary by cubic

Fixes fishtape path resolution in fish tests to stop "Unknown command" errors in CI. Also pins Elixir to elixir_1_19 for consistent builds.

• Bug Fixes

  • Load fish functions via ../../home-manager/programs/fish/functions instead of (status dirname).
  • Aligns with fishtape running tests from the test file’s directory, restoring CI reliability.

• Dependencies

  • Switch elixir to elixir_1_19 in Home Manager for a stable toolchain.