That was the resolution that all members, both Republicans and Democrats voted yes on. Please note that it does not ask for a public release, that would be against the law:
"
(1) calls for the public release of any report, including findings, Special Counsel Mueller provides to the Attorney General, except to the extent the public disclosure of any portion thereof is expressly prohibited by law; and
(2) calls for the full release to Congress of any report, including findings, Special Counsel Mueller provides to the Attorney General."
Demanding that the full report be released to the Congress only does not appear to break that law. After all they would be the one's trying and convicting the President. That makes them agents of the government responsible for the enforcement of the law, that is covered by the Exceptions.