Warning when building a package using the plugin with Swift 5.9.

[thomasvl]

In adding Swift 5.9 to the CI for swift-protobuf, we noticed some warning coming from the plugin compile:

https://github.com/apple/swift-protobuf/actions/runs/6249612455/job/16966661520?pr=1459

/__w/swift-protobuf/swift-protobuf/main/.build/checkouts/swift-docc-plugin/Plugins/Swift-DocC Convert/Symbolic Links/SharedPackagePluginExtensions/PackageExtensions.swift:31:17: warning: switch covers known cases, but 'TargetDependency' may have additional unknown values
                switch dependency {
                ^
/__w/swift-protobuf/swift-protobuf/main/.build/checkouts/swift-docc-plugin/Plugins/Swift-DocC Convert/Symbolic Links/SharedPackagePluginExtensions/PackageExtensions.swift:31:17: note: handle unknown values using "@unknown default"
                switch dependency {
                ^
[1/1] Compiling plugin Swift-DocC
/__w/swift-protobuf/swift-protobuf/main/.build/checkouts/swift-docc-plugin/Plugins/Swift-DocC Preview/Symbolic Links/SharedPackagePluginExtensions/PackageExtensions.swift:31:17: warning: switch covers known cases, but 'TargetDependency' may have additional unknown values
                switch dependency {
                ^
/__w/swift-protobuf/swift-protobuf/main/.build/checkouts/swift-docc-plugin/Plugins/Swift-DocC Preview/Symbolic Links/SharedPackagePluginExtensions/PackageExtensions.swift:31:17: note: handle unknown values using "@unknown default"
                switch dependency {
                ^

Checklist

• [ ] If possible, I've reproduced the issue using the main branch of this package.
• [x] This issue hasn't been addressed in an existing GitHub issue.

Expected behavior

Clean compile.

Actual behavior

Warning generated.

Steps to Reproduce

Simply doing a build should produce the warnings.

Swift-DocC Plugin Version Information

Swift-DocC plugin version: 1.3.0 Swift Compiler version: 5.9

[d-ronnqvist]

This looks like it was already fixed by adding @unknown default here.