Fix cfg_select! compile error in panic handler

[greeble-dev]

Objective

Ran into this after #23896:

> cargo build -p bevy_app --no-default-features --features "std"

error: none of the predicates in this `cfg_select` evaluated to true
  --> crates\bevy_app\src\panic_handler.rs:46:17
   |
46 | /                 cfg_select! {
47 | |                     all(target_arch = "wasm32", feature = "web") => {
48 | |                         // This provides better panic handling in JS engines (displays the panic message and improves the backtrace).
49 | |                         std::panic::set_hook(alloc::boxed::Box::new(console_error_panic_hook::hook));
...  |
58 | |                 }
   | |_________________^

Solution

Add a fallback clause. Also did a quick scan to confirm that other cases of cfg_select! were fine.

Testing

cargo build -p bevy_app --no-default-features --features "std"
cargo build -p bevy_app --no-default-features
cargo build -p bevy_app
cargo run --example 3d_scene
cargo run --example 3d_scene --target wasm32-unknown-unknown --features "webgpu"