Set ExpectContinue on redirect messages too

Apply Options.Expect100Continue to HttpRequestMessages created during
redirect handling, matching the behavior of the initial request.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: alexeyzimarev

src/RestSharp/RestClient.Async.cs

@@ -273,9 +273,10 @@ HttpRequestMessage CreateRedirectMessage(
         bool verbChangedToGet
     ) {
         var redirectMessage = new HttpRequestMessage(httpMethod, url);
-        redirectMessage.Version              = request.Version;
-        redirectMessage.Headers.Host         = Options.BaseHost;
-        redirectMessage.Headers.CacheControl = request.CachePolicy ?? Options.CachePolicy;
+        redirectMessage.Version                = request.Version;
+        redirectMessage.Headers.Host           = Options.BaseHost;
+        redirectMessage.Headers.CacheControl   = request.CachePolicy ?? Options.CachePolicy;
+        redirectMessage.Headers.ExpectContinue = Options.Expect100Continue;
 
         if (!verbChangedToGet && redirectOptions.ForwardBody) {
             var redirectContent = new RequestContent(this, request);