build: split the SwiftDocCUtilitiesTest for Windows

We need to replicate the target definition to exclude some files when
building for Windows as they depend on NIO to create the PreviewServer.
Rather than adding the files and conditionally removing the content,
remove thee files from being built.

Package.swift

@@ -105,7 +105,7 @@ let package = Package(
 
 // Command-line tool library
 #if os(Windows)
-package.targets.append(
+package.targets.append(contentsOf: [
     .target(
         name: "SwiftDocCUtilities",
         dependencies: [
@@ -120,10 +120,29 @@ package.targets.append(
             "ArgumentParsing/Subcommands/Preview.swift",
         ],
         swiftSettings: swiftSettings
-    )
-)
+    ),
+    .testTarget(
+        name: "SwiftDocCUtilitiesTests",
+        dependencies: [
+            .target(name: "SwiftDocCUtilities"),
+            .target(name: "SwiftDocC"),
+            .target(name: "SwiftDocCTestUtilities"),
+        ],
+        exclude: [
+            // PreviewServer requires NIO which cannot support non-POSIX platforms.
+            "ArgumentParsing/PreviewSubcommandTests.swift",
+            "PreviewActionIntegrationTests.swift",
+            "PreviewServer",
+        ],
+        resources: [
+            .copy("Test Resources"),
+            .copy("Test Bundles"),
+        ],
+        swiftSettings: swiftSettings
+    ),
+])
 #else
-package.targets.append(
+package.targets.append(contentsOf: [
     .target(
         name: "SwiftDocCUtilities",
         dependencies: [
@@ -132,11 +151,7 @@ package.targets.append(
             .product(name: "ArgumentParser", package: "swift-argument-parser")
         ],
         swiftSettings: swiftSettings
-    )
-)
-#endif
-
-package.targets.append(
+    ),
     .testTarget(
         name: "SwiftDocCUtilitiesTests",
         dependencies: [
@@ -149,8 +164,9 @@ package.targets.append(
             .copy("Test Bundles"),
         ],
         swiftSettings: swiftSettings
-    )
-)
+    ),
+])
+#endif
 
 // If the `SWIFTCI_USE_LOCAL_DEPS` environment variable is set,
 // we're building in the Swift.org CI system alongside other projects in the Swift toolchain and