1.12.0 - Update to Swift 5.9

What's Changed

Update to Swift 5.9 by @fpseverino in #134

• Update swift-tools-version to 5.9
• Add common swiftSettings to targets
• Fix unhandled files warnings
  • Templates folder in test target; added to target’s resources
  • Docs.docc folder in main target; updating swift-tools-version fixes it
• Lock was deprecated in favour of NIOLock
• Add MUSL and iOS in CI

This patch was released by @0xTim

Full Changelog: 1.11.1...1.12.0