Swift 5.8 compilation failure `/Package.swift:4:8: error: no such module 'CompilerPluginSupport'` -> ⚠️ SemVer break

As per `Package.swift` we support Swift 5.8 here. But an actual compilation fails with

```
error: Invalid manifest (compiled with: ["/usr/bin/swiftc", "-vfsoverlay", "/tmp/TemporaryDirectory.ImEdbq/vfs.yaml", "-L", "/usr/lib/swift/pm/ManifestAPI", "-lPackageDescription", "-Xlinker", "-rpath", "-Xlinker", "/usr/lib/swift/pm/ManifestAPI", "-swift-version", "5", "-I", "/usr/lib/swift/pm/ManifestAPI", "-package-description-version", "5.8.0", "/Package.swift", "-Xfrontend", "-disable-implicit-concurrency-module-import", "-Xfrontend", "-disable-implicit-string-processing-module-import", "-o", "/tmp/TemporaryDirectory.qU2Iyh/swift-async-algorithms-manifest"])
/Package.swift:4:8: error: no such module 'CompilerPluginSupport'
import CompilerPluginSupport
^ in https://github.com/apple/swift-async-algorithms.git

```

This is a SemVer break so needs urgent fixing.

Start with Package.swift and reproduce the manifest compilation using Swift 5.8, focusing on the reported CompilerPluginSupport import failure. Check the package manifest's declared Swift tools version and verify the chosen compatibility fix by confirming that the manifest compiles successfully with Swift 5.8.

Written by the indexing model from the issue text.