Fix partially formatted if chains in attributes (#2999)

packages/core/tests/conditional_formatted_attributes.rs

@@ -0,0 +1,13 @@
+use dioxus::prelude::*;
+
+/// Make sure that rsx! handles conditional attributes with one formatted branch correctly
+/// Regression test for https://github.com/DioxusLabs/dioxus/issues/2997
+#[test]
+fn partially_formatted_conditional_attribute() {
+    let width = "1px";
+    _ = rsx! {
+        div {
+            width: if true { "{width}" } else { "100px" }
+        }
+    };
+}