Update to Swift 5.9 release

[finestructure]

• install new Xcode version on builders
  • Xcode-15.0.0 (mb6)
  • Xcode-14.3.1 (mb5)
• Update spi-images https://gitlab.com/finestructure/spi-images/-/merge_requests/12
• make sure SPIManifest SwiftVersion.latestRelease is pointing to the desired Swift version (for doc builds) https://github.com/SwiftPackageIndex/SPIManifest/pull/33/files
• update builder https://gitlab.com/finestructure/swiftpackageindex-builder/-/merge_requests/221
  • SwiftVersion.xcodeVersion
  • SwiftVersion.dockerImage doesn't need changing, this is done via spi-images
• update server Swift 5.9 release base image #2632
  • SwiftVersion.xcodeVersion
• remove old Xcode version from builders
• update base image in package list Update base image to swift:5.9-jammy PackageList#5238
• update base image in validator Test with swift:5.9-jammy PackageList-Validator#50

[finestructure]

@daveverwer NB, I'm bumping the builder's Xcode versions to Xcode-15.0.0 and Xcode-14.3.1. We were still on 14.3.0.

[finestructure]

We're now building with 5.9 release. Keeping this issue open until the cleanup tasks are complete.