Use CowArc::Static (#14981)

# Objective

- There's one occurence of `CowArc::Borrow` that wraps '&'static str`

## Solution

- Replaces it with `CowArc::Static`. I don't think this change is
important but I can't unsee it:)

## Testing

- `cargo check` compiles fine

crates/bevy_asset/src/server/mod.rs

@@ -415,7 +415,7 @@ impl AssetServer {
  ) -> Handle<LoadedUntypedAsset> {
  let path = path.into().into_owned();
  let untyped_source = AssetSourceId::Name(match path.source() {
- AssetSourceId::Default => CowArc::Borrowed(UNTYPED_SOURCE_SUFFIX),
+ AssetSourceId::Default => CowArc::Static(UNTYPED_SOURCE_SUFFIX),
  AssetSourceId::Name(source) => {
  CowArc::Owned(format!("{source}--{UNTYPED_SOURCE_SUFFIX}").into())
  }