Pin dependencies for py36 compatibility [wallaby 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)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7826a64) 82.27% compared to head (300c5bb) 82.27%. Report is 1 commits behind head on stable/wallaby.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## stable/wallaby #634 +/- ## =============================================== Coverage 82.27% 82.27% =============================================== Files 30 30 Lines 2776 2776 =============================================== Hits 2284 2284 Misses 492 492 ```

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