Release v3.8.6 (#1636)

* Prepare release v3.8.6

* Update test fixtures with the new nix-installer version

* flake.lock: Update

Flake lock file updates:

• Updated input 'determinate':
    'https://api.flakehub.com/f/pinned/DeterminateSystems/determinate/3.8.5/01987740-2f8d-724e-be76-f9fdc4169391/source.tar.gz?narHash=sha256-IxwxFY1vD3K1lNi7zKb3O31K/gjB0QRs5G%2B66R5uKXc%3D' (2025-08-04)
  → 'https://api.flakehub.com/f/pinned/DeterminateSystems/determinate/3.8.6/0198c8e2-c539-7713-a109-3ff0e73574dd/source.tar.gz?narHash=sha256-QNc4TY7l/NIkPpuFSXGAUnAFpsz4GiYAwGFyYXEJ9lc%3D' (2025-08-20)
• Updated input 'determinate/determinate-nixd-aarch64-darwin':
    'https://install.determinate.systems/determinate-nixd/tag/v3.8.5/macOS?narHash=sha256-qZLIbSP6ic9/ozzFP0QqSk5CcQdbQ4iJHuCd03wV4i8%3D'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.8.6/macOS?narHash=sha256-TXc1t7wbUtzwyytrZMR9SoTsUdoXatDf45aoNndaonY%3D'
• Updated input 'determinate/determinate-nixd-aarch64-linux':
    'https://install.determinate.systems/determinate-nixd/tag/v3.8.5/aarch64-linux?narHash=sha256-QK06CsX8jhocJlUmv%2BLGJL%2B67OqkaFutt4kyU9VYshE%3D'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.8.6/aarch64-linux?narHash=sha256-MaD8woffmbfytD/1Ism5xLhonTlCzXyTU6TmVpin2vU%3D'
• Updated input 'determinate/determinate-nixd-x86_64-linux':
    'https://install.determinate.systems/determinate-nixd/tag/v3.8.5/x86_64-linux?narHash=sha256-WewOOmK0rZ7yDBaA1xie1wHYTMkB96scY4Fjt6MPxfQ%3D'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.8.6/x86_64-linux?narHash=sha256-cAXTuExL/7cmdzXM0vJLuHvExpjmv39%2BvWwgJyKbZnA%3D'
• Updated input 'nix':
    'https://api.flakehub.com/f/pinned/DeterminateSystems/nix-src/3.8.5/0198772e-696e-72c6-9382-7ad2a9198f03/source.tar.gz?narHash=sha256-xVsqhMfsQzjf4XDO/GHVyk/D760uqlnOQ1NZ8Iyvpr0%3D' (2025-08-04)
  → 'https://api.flakehub.com/f/pinned/DeterminateSystems/nix-src/3.8.6/0198c717-3128-706c-95f8-49294f65c4b7/source.tar.gz?narHash=sha256-aHMByu8/6cJsUYffUgM4DnZRiLfBpQM0C9Wa3dCJ87o%3D' (2025-08-20)

* Update Cargo dependencies

* Set Cargo.toml package.version to 3.8.6

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]