Bump `walrus` to v0.20 #1212

Job	Run time
Rustfmt	8s
Rustfmt	8s
Check	1m 41s
Check	1m 41s
Clippy	5m 55s
Clippy	5m 55s
Run wasm-bindgen crate tests with multithreading enabled	2m 29s
Run wasm-bindgen crate tests with multithreading enabled	2m 29s
Run wasm-bindgen crate tests (unix)	11m 7s
Run wasm-bindgen crate tests (unix)	11m 7s
build_benchmarks	1m 17s
build_benchmarks	1m 17s
build_examples	4m 45s
build_examples	4m 45s
build_nightly	2m 33s
build_nightly	2m 33s
Verify that web-sys is compiled correctly	1m 18s
Verify that web-sys is compiled correctly	1m 18s
Build and test the deno example	1m 14s
Build and test the deno example	1m 14s
Run js-sys crate tests	3m 24s
Run js-sys crate tests	3m 24s
Run native tests	3m 26s
Run native tests	3m 26s
Test TypeScript output of wasm-bindgen	1m 31s
Test TypeScript output of wasm-bindgen	1m 31s
Run UI compile-fail tests	3m 42s
Run UI compile-fail tests	3m 36s
Run web-sys crate tests	5m 21s
Run web-sys crate tests	5m 21s
Run wasm-bindgen-webidl crate tests	3m 25s
Run wasm-bindgen-webidl crate tests	3m 25s
dist_linux_aarch64_gnu	4m 18s
dist_linux_aarch64_gnu	4m 18s
dist_linux_x86_64_musl	3m 12s
dist_linux_x86_64_musl	3m 12s
dist_macos_aarch64	3m 33s
dist_macos_aarch64	3m 33s
dist_macos_x86_64	5m 2s
dist_macos_x86_64	5m 2s
dist_windows	4m 51s
dist_windows	4m 51s
doc_api	1m 26s
doc_api	1m 26s
doc_book	21s
doc_book	21s
test_examples	3m 4s
test_examples	3m 4s
deploy	1m 19s
deploy	1m 19s
	2h 40m 38s

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