(Tiny PR) Show `JsValue` is not Send/Sync explicitly #1592

Job	Run time
Clippy	1m 45s
Run wasm-bindgen crate tests (unix)	16s
Verify that web-sys is compiled correctly	46s
Rustfmt	5s
Run js-sys crate tests	15s
Check	17s
Run native tests	14s
Run wasm-bindgen crate tests with multithreading enabled	36s
Run web-sys crate tests	31s
Run wasm-bindgen-webidl crate tests	35s
build_benchmarks	12s
build_examples	1m 21s
build_nightly	47s
dist_linux_aarch64_gnu	2m 44s
dist_linux_x86_64_musl	2m 16s
dist_macos_aarch64	3m 46s
dist_macos_x86_64	2m 37s
dist_windows	3m 35s
Build and test the deno example	18s
doc_book	31s
Test TypeScript output of wasm-bindgen	17s
Run UI compile-fail tests	1m 56s
doc_api	16s
test_examples	0s
deploy	0s
	25m 56s

Provide feedback