ci: fix rust:lint job (#1983)

Recently, CI jobs started failing on the `rust:lint` step.
One suitable workaround was to ignore the questionable lints
via Cargo.toml:

```
[lints.rust]
unexpected_cfgs = { level = "warn", check-cfg = ['cfg(wasm_bindgen_unstable_test_coverage)'] }
```

This seems to resolve. I also tried bumping the `wasm-bindgen` dep to
0.2.100, which didn't resolve on its own. See related discussion in [0].

[0] rustwasm/wasm-bindgen#4283

packages/wasm/crate/Cargo.toml

@@ -51,3 +51,6 @@ web-sys = { version = "0.3.70", features = ["console"] }
 [dev-dependencies]
 wasm-bindgen-test = "0.3.43"
 serde_json = "1.0.128"
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(wasm_bindgen_unstable_test_coverage)'] }