fix: Use explicit Package.Dependency type to avoid Swift 6.2.3 circular reference bug

The pattern `.package(url:...)` inside `package.dependencies.append()` causes
Swift 6.2.3 to confuse the member lookup with the `package` variable, resulting
in a "circular reference" error.

The fix uses the explicit type `Package.Dependency.package(url:...)` to avoid
this ambiguity.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Stijn Willems

Package.swift

@@ -107,7 +107,8 @@ for index in package.targets.indices {
 
 #if !os(Windows)
     // Add the documentation compiler plugin if possible
+    // NB: Use explicit type to avoid Swift 6.2.3 circular reference bug
     package.dependencies.append(
-        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")
+        Package.Dependency.package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0")
     )
 #endif