fix: user agent regression, closes #1396 (#1397)

regression from #1384

Author: lucasfernog

.changes/fix-user-agent-regression.md

@@ -0,0 +1,5 @@
+---
+"wry": patch
+---
+
+Fix `with_user_agent` regression.

src/lib.rs

@@ -907,7 +907,7 @@ impl<'a> WebViewBuilder<'a> {
   /// see https://learn.microsoft.com/en-us/microsoft-edge/webview2/release-notes/archive?tabs=dotnetcsharp#10790-prerelease
   pub fn with_user_agent(self, user_agent: impl Into<String>) -> Self {
     self.and_then(|mut b| {
-      b.attrs.html = Some(user_agent.into());
+      b.attrs.user_agent = Some(user_agent.into());
       Ok(b)
     })
   }