update ubuntu python .deb requirement for dataclasses

Summary: We have dataclasses dependency now in eden_scm, which means python 3.7 or later

Reviewed By: quark-zju

Differential Revision: D33713759

fbshipit-source-id: 6f915238326201d7408f885804714981505b7fa8

build/fbcode_builder/manifests/python

@@ -5,7 +5,8 @@ name = python
 python3
 python3-devel
 
-[debs]
+# eden_scm needs dataclasses which arrive in 3.7, and the bionic python is 3.6
+[debs.not(all(distro=ubuntu,distro_vers="18.04"))]
 python3-all-dev
 
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