Release v3.15.2 (#1747)

* Prepare release v3.15.2

* Update test fixtures with the new nix-installer version

* Update Determinate Nix release to 3.15.2

* flake.lock: Update

Flake lock file updates:

• Updated input 'determinate':
    'https://api.flakehub.com/f/pinned/DeterminateSystems/determinate/3.15.1/019b4e8a-dc22-75db-aef5-a447efbb1a13/source.tar.gz' (2025-12-24)
  → 'https://api.flakehub.com/f/pinned/DeterminateSystems/determinate/3.15.2/019bde7d-0725-73ef-9705-498c50ef6e00/source.tar.gz' (2026-01-21)
• Updated input 'determinate/determinate-nixd-aarch64-darwin':
    'https://install.determinate.systems/determinate-nixd/tag/v3.15.1/macOS'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.15.2/macOS'
• Updated input 'determinate/determinate-nixd-aarch64-linux':
    'https://install.determinate.systems/determinate-nixd/tag/v3.15.1/aarch64-linux'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.15.2/aarch64-linux'
• Updated input 'determinate/determinate-nixd-x86_64-linux':
    'https://install.determinate.systems/determinate-nixd/tag/v3.15.1/x86_64-linux'
  → 'https://install.determinate.systems/determinate-nixd/tag/v3.15.2/x86_64-linux'
• Updated input 'nix':
    'https://api.flakehub.com/f/pinned/DeterminateSystems/nix-src/3.15.1/019b4e84-d036-75db-b6c6-6bc2e2035c53/source.tar.gz' (2025-12-24)
  → 'https://api.flakehub.com/f/pinned/DeterminateSystems/nix-src/3.15.2/019bde75-b4ee-74b2-a812-28dc2ee83d58/source.tar.gz' (2026-01-21)
• Updated input 'nixpkgs':
    'https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.914755%2Brev-a6531044f6d0bef691ea18d4d4ce44d0daa6e816/019b4613-7276-7c80-8e57-953e4698fb6e/source.tar.gz' (2025-12-21)
  → 'https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.928726%2Brev-e4bae1bd10c9c57b2cf517953ab70060a828ee6f/019bc8c9-d277-7e35-b3d9-c36e1fdbfb5a/source.tar.gz' (2026-01-16)

* Update Cargo dependencies

* Set Cargo.toml package.version to 3.15.2

---------

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

Author: github-actions[bot]