restrict fbthrift python dependency to fix watchman-diag

Reviewed By: singhsrb

Differential Revision: D33982894

fbshipit-source-id: 5ec3f1555a551f3931983fde844346293704231c

build/fbcode_builder/manifests/fbthrift

@@ -23,8 +23,9 @@ libsodium
 python-six
 zstd
 
-[dependencies.not(os=windows)]
-# python doesn't build on Windows yet
+[dependencies.os=linux]
+# python doesn't build on Windows yet and this causes python3 shebangs to
+# expand to a non-portable path on macOS
 python
 
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