fix(init): enable yamllint indentation rule

[zeitlinger]

Summary

Converges generated .github/config/.yamllint.yml on indentation: enable instead of the legacy nested spaces: 2 shape.

The generator test now asserts the exact generated config so this does not drift back to ad hoc variants.

Validation

• cargo test generate_yamllint_config_writes_file
• FLINT_CASES=general/init-rust cargo test cases
• FLINT_CASES=ryl mise exec -- cargo test cases
• mise run lint:fix
• mise run lint
• mise exec -- cargo test --bins -- --skip registry::tests::all_registry_binaries_found

Note: full cargo test --bins is blocked in this environment by missing dotnet-format.

[Copilot]

Pull request overview

This PR updates the generated yamllint configuration to use the canonical indentation: enable rule form (instead of the legacy nested spaces: 2 form) and hardens the generator test to prevent future drift in the generated .github/config/.yamllint.yml.

Changes:

• Update .yamllint.yml fixtures to use indentation: enable.
• Update the init generator (generate_yamllint_config) to emit indentation: enable.
• Strengthen the generator test to assert the full generated file content exactly.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/init/config_files.rs	Changes yamllint config generation to emit indentation: enable.
src/init/tests.rs	Updates test to assert exact .yamllint.yml output, preventing config drift.
.github/config/.yamllint.yml	Aligns repo yamllint config with indentation: enable.
tests/cases/general/init-rust/test.toml	Updates init-rust golden output to match new generated yamllint config.
tests/cases/ryl/clean/files/.github/config/.yamllint.yml	Updates ryl clean fixture to the new indentation rule shape.
tests/cases/ryl/failure/files/.github/config/.yamllint.yml	Updates ryl failure fixture to the new indentation rule shape.

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