Don't print `=` on empty attribute when spreading #941

Job	Run time
get-leptos-changed / Detect Source Change	6s
CI (integrations/viz) / Run ci (nightly)	16m 36s
CI (integrations/actix) / Run ci (nightly)	20m 13s
CI (integrations/utils) / Run ci (nightly)	15m 48s
CI (integrations/axum) / Run ci (nightly)	20m 16s
CI (leptos) / Run ci (nightly)	1h 38m 45s
CI (leptos_dom) / Run ci (nightly)	28m 14s
CI (leptos_hot_reload) / Run ci (nightly)	17m 20s
CI (leptos_config) / Run ci (nightly)	16m 16s
CI (leptos_macro) / Run ci (nightly)	23m 48s
CI (leptos_reactive) / Run ci (nightly)	50m 24s
CI (meta) / Run ci (nightly)	16m 43s
CI (router) / Run ci (nightly)	18m 30s
CI (server_fn) / Run ci (nightly)	16m 20s
CI (server_fn_macro) / Run ci (nightly)	18m 18s
CI (server_fn/server_fn_macro_default) / Run ci (nightly)	14m 2s
CI (leptos_server) / Run ci (nightly)	26m 0s
	6h 57m 39s

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