chore: fix swift build fail on swift 5.5

Author: soumyamahunt

Package.swift

@@ -2,6 +2,20 @@
 
 import PackageDescription
 
+let dependencies: [Package.Dependency]
+#if compiler(>=5.6) && swift(>=5.6)
+dependencies = [
+    .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.0"),
+    .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
+    .package(url: "https://github.com/apple/swift-format", from: "0.50600.1"),
+]
+#else
+dependencies = [
+    .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.0"),
+    .package(url: "https://github.com/apple/swift-format", from: "0.50600.1"),
+]
+#endif
+
 let package = Package(
     name: "AsyncObject",
     platforms: [
@@ -16,11 +30,7 @@ let package = Package(
             targets: ["AsyncObject"]
         ),
     ],
-    dependencies: [
-        .package(url: "https://github.com/apple/swift-collections.git", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-format", from: "0.50600.1"),
-    ],
+    dependencies: dependencies,
     targets: [
         .target(
             name: "AsyncObject",