build(deps): bump socket2 from 0.3.12 to 0.3.15
Bumps [socket2](https://github.com/alexcrichton/socket2-rs) from 0.3.12 to 0.3.15.
- [Release notes](https://github.com/alexcrichton/socket2-rs/releases)
- [Commits](https://github.com/alexcrichton/socket2-rs/compare/0.3.12...v0.3.15)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>