Bump requirements of nested benchmarking package

[lorentey]

Let's adopt the new swift-collections-benchmark tag.

• swift-collections-benchmark 0.0.4
• Swift 6.1 minimum toolchain version
• macOS 15 minimum deployment target

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• I've updated the documentation if necessary.

[lorentey]

@swift-ci test