allow #[verifier(external_body)] again on consts #6067

Job	Run time
smoke-test-and-release-macos-x86	9m 57s
smoke-test-and-release-linux	6m 31s
fmt	55s
smoke-test-and-release-windows	8m 53s
test-and-release-macos	11m 7s
test-and-release-macos (record-history)	3m 16s
test-and-release-macos (no-std)	2m 55s
test-and-release-macos (no-alloc)	2m 50s
test-and-release-macos (singular)	3m 12s
test-and-release-macos (cvc5)	2m 34s
release	0s
	52m 10s

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