Reject env.json if there are duplicate export names, fix #189 (#994) #2593

Job	Run time
build-and-test (ubuntu-latest, wasm32-unknown-unknown, false)	5m 53s
build-and-test (ubuntu-latest, x86_64-unknown-linux-gnu, true)	12m 15s
cargo-deny (advisories)	3m 23s
cargo-deny (bans licenses sources)	3m 1s
fmt	9s
rust-analyzer-compat	11m 52s
publish-dry-run (ubuntu-latest, wasm32-unknown-unknown) / publish-dry-run	1m 53s
publish-dry-run (ubuntu-latest, x86_64-unknown-linux-gnu) / publish-dry-run	1m 36s
complete	2s
	40m 4s

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