fix: allow duplicate additionalGids

[saku3]

Description

In runc v1.3.0, the behavior has changed when specifying duplicate additionalGids.
To align with this change, we are updating the behavior of additionalGids handling in youki accordingly.

For more details, please refer to the following issue.
opencontainers/runc#4769 (comment)

Type of Change

• [] Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test updates
• CI/CD related changes
• Other (please describe):
  compatibility with runc

Testing

• Added new unit tests
• Added new integration tests
• Ran existing test suite
• Tested manually (please provide steps)

Related Issues

Fixes #

Additional Context

[Copilot]

Pull Request Overview

This PR updates Youki’s handling of duplicate supplementary group IDs (additionalGids) to match runc v1.3.0 by preserving duplicates instead of deduplicating them. It also adapts existing tests to conditionally skip the duplicate-GID check when running under runc.

• Remove HashSet-based deduplication in set_supplementary_gids
• Update unit tests to expect preserved duplicates
• Introduce ConditionalTest to skip duplicate-GID tests on runc

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/contest/contest/src/tests/process_user/process_user_test.rs	Switch to ConditionalTest and adjust duplicate-gid test logic
crates/libcontainer/src/process/init/process.rs	Remove duplicate filtering and add unit test for duplicate GIDs

Comments suppressed due to low confidence (1)

tests/contest/contest/src/tests/process_user/process_user_test.rs:69

• [nitpick] The comment mentions skipping only runc v1.1, but the condition !is_runtime_runc() skips on any runc runtime. Consider clarifying the comment (or the condition) to accurately reflect that all runc runtimes are excluded.

    // The current CI for Youki uses runc 1.1, so this will be skipped.

[utam0k]

This leads to a breaking change.