macOS: Fix WebView print hang

At least under macOS 11 calling just runOperation: hangs, so use
runOperationModalForWindow: instead.

Closes https://github.com/wxWidgets/wxWidgets/pull/2198

Closes #19063.

src/osx/webview_webkit.mm

@@ -271,7 +271,8 @@ void wxWebViewWebKit::Print()
         [op setShowsProgressPanel: false];
     }
     // Print it.
-    [op runOperation];
+    [op runOperationModalForWindow:m_webView.window
+                          delegate:nil didRunSelector:nil contextInfo:nil];
 }
 
 void wxWebViewWebKit::SetEditable(bool WXUNUSED(enable))