fix(syn-solidity): allow some duplicate attributes #1147

Job	Run time
feature-checks	2m 40s
docs	57s
clippy	1m 39s
fmt	13s
miri --no-default-features	4m 21s
test stable --no-default-features	1m 39s
miri	3m 44s
wasm	47s
test stable	46s
miri --all-features	4m 9s
test stable --all-features	1m 51s
test beta --no-default-features	1m 17s
test beta	1m 28s
test beta --all-features	1m 26s
test nightly --no-default-features	2m 48s
test nightly	2m 53s
test nightly --all-features	3m 14s
test 1.65 --no-default-features	53s
test 1.65	36s
	37m 21s

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