Have OSS getdeps.py pull code from 'main' (instead of 'master') until all repos are migrated

Summary: getdeps.py pulls repos from master branch by default. For FBOSS force it to pull from 'main'

Reviewed By: shri-khare

Differential Revision: D30857755

fbshipit-source-id: 9891f1ddc08c8f13bdcb00385e1ad4516a84776c

build/fbcode_builder/manifests/fboss

@@ -6,6 +6,7 @@ shipit_fbcode_builder = true
 
 [git]
 repo_url = https://github.com/facebook/fboss.git
+rev = main
 
 [build.os=linux]
 builder = cmake