Reduce platform requirements

Sources/Push/PushClient.swift

@@ -145,6 +145,39 @@ public final class PushClient {
         var request = URLRequest(url: server.appendingPathComponent(route.rawValue))
         request.httpBody = bodyData
         request.httpMethod = "POST"
+
+        if #available(iOS 15.0, *) {
+            return await post(request)
+        } else {
+            return await withCheckedContinuation { continuation in
+                postRequest(request) { data in
+                    continuation.resume(returning: data)
+                }
+            }
+        }
+    }
+
+    private func postRequest(_ request: URLRequest, completion: @escaping (Data?) -> Void) {
+        URLSession.shared.dataTask(with: request) { data, response, error in
+            if let error = error {
+                print("Failed with error: \(error)")
+                completion(nil)
+            }
+            guard let httpResponse = response as? HTTPURLResponse else {
+                completion(nil)
+                return
+            }
+            guard httpResponse.statusCode == 200 else {
+                print("Failed with code: \(httpResponse.statusCode)")
+                completion(nil)
+                return
+            }
+            completion(data)
+        }.resume()
+    }
+
+    @available(iOS 15.0, *)
+    private func post(_ request: URLRequest) async -> Data? {
         do {
             let (data, response) = try await URLSession.shared.data(for: request)
             guard let httpResponse = response as? HTTPURLResponse else {