Using `Rc<dyn AnyValue>` as an attribute value causes unreachable code to be hit and panics

**Problem**

```
04:09:20 [web] panicked at /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/dioxus-web-0.7.3/src/mutations.rs:211:18:
internal error: entered unreachable code

Stack:

Error
at http://127.0.0.1:33870/wasm/languna.js:968:25
at logError (http://127.0.0.1:33870/wasm/languna.js:1834:18)
at __wbg_new_00868141024267bc (http://127.0.0.1:33870/wasm/languna.js:967:57)
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[25102]:0x3f2a79
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[14529]:0x383d25
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[3959]:0x244f92
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[19054]:0x3bed22
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[4762]:0x2701f4
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[8443]:0x2ff5bd
at http://127.0.0.1:33870/wasm/languna_bg.wasm:wasm-function[25573]:0x3f419a
```

Line: https://github.com/DioxusLabs/dioxus/blob/d01a820b6f6921ecb6ae459fa85de7bc575a9133/packages/web/src/mutations.rs#L211

Reproducible fragment

```rust
let val = Rc::new(String::new()) as Rc;
rsx! {
iframe { srcdoc: val }
}
```

Originally I wanted to use `Rc` instead of `Rc` but it does not implement `IntoAttributeValue` since `str` is not `Sized`. So that is what lead me to this situation.

It seems the temporary solution is to use a `String` with cloning. For my use case, it is a fairly large `String` but it won't be hit often so it is not too big of a deal.

**Expected behavior**

Works with no panic or compiler error.

**Environment:**

- Dioxus version: v0.7.3
- Rust version: 1.93
- OS info: linux
- App platform: web