[naga] Require hashbrown's serde feature as a dev-dependency.

Add `hashbrown` with the `"serde"` feature as a development dependency
for Naga. Regardless of whether Naga's `deserialize` feature is
enabled, the snapshot tests need to deserialize parameters saved in
files as RON text.

It would also suffice to use `std::collections::HashSet` in the
snapshot tests, although we would need to build a `naga::FashHashSet`
from the std `HashSet` at one point. Adding the dev-dependency seems
slightly simpler.

Fixes #7308.

naga/Cargo.toml

@@ -117,3 +117,4 @@ ron = "0.8.0"
 rspirv = { version = "0.11", git = "https://github.com/gfx-rs/rspirv", rev = "b969f175d5663258b4891e44b76c1544da9661ab" }
 serde = { workspace = true, features = ["default", "derive"] }
 spirv = { version = "0.3", features = ["deserialize"] }
+hashbrown = { workspace = true, features = ["serde"] }