Add snapshot test for gradient_extend scene #1804

Job	Run time
cargo check (aarch64-android)	24s
cargo check (msrv) (wasm32)	41s
cargo clippy (windows-latest)	2m 19s
cargo check (msrv) (windows-latest)	1m 23s
cargo clippy (macos-latest)	1m 8s
cargo check (msrv) (macos-latest)	41s
cargo clippy (ubuntu-latest)	1m 39s
cargo clippy (wasm32)	1m 31s
cargo check (msrv) (ubuntu-latest)	51s
cargo doc	1m 44s
Prime LFS Cache	9s
formatting	21s
cargo test (wasm32)	28s
typos	4s
cargo test (windows-latest)	1m 43s
cargo test (macos-latest)	1m 35s
cargo test (ubuntu-latest)	4m 17s
	20m 58s

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