Summary: CentOS Stream 8's cmake 3.20.2 boost rules don't find the system boost with just BOOST_ROOT_1_78_0 (make sense, the system boost is 1.69),  so set BOOST_ROOT_1_69_0 as well

Reviewed By: chadaustin

Differential Revision: D34000244

fbshipit-source-id: 73df3b6b9f1c091fd70fd61bc7169c5f77ed632b