Pin dependencies for py36 compatibility [victoria backport]

[freyes]

macaroonbakery in version 1.3.4 started depending on protobuf>3.20 which it's not compatible with python 3.6, so this change pins macaroonbakery to 1.3.2 which was the last release compatible with older versions of protobuf.

For more details see:

• https://github.com/go-macaroon-bakery/py-macaroon-bakery/pull/92
• https://github.com/protocolbuffers/protobuf/issues/10076

It's worth to mention that there is no protobuf-4.0, it goes from 3.20 to 4.21 - https://pypi.org/project/protobuf/#history

(cherry picked from commit a8e4de518f32503e788547e78ff2f609c0275dc3) (cherry picked from commit 300c5bbefb1228e20d53226951662074bbb729d4)