set BOOST_ROOT_1_69_0 as well as BOOST_ROOT_1_78_0

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

build/fbcode_builder/manifests/boost

@@ -10,6 +10,8 @@ url = https://boostorg.jfrog.io/artifactory/main/release/1.78.0/source/boost_1_7
 sha256 = f22143b5528e081123c3c5ed437e92f648fe69748e95fa6e2bd41484e2986cc3
 
 [preinstalled.env]
+# Here we list the acceptable versions that cmake needs a hint to find
+BOOST_ROOT_1_69_0
 BOOST_ROOT_1_78_0
 
 [debs]