Avoid broken macaroonbakery release

[coreycb]

macaroonbakery 1.3.3 has a broken protobuf dependency, add a requirement to avoid that specific release:
go-macaroon-bakery/py-macaroon-bakery#94

(cherry picked from commit 8be4948)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (44333de) 89.41% compared to head (7766837) 89.41%.

Additional details and impacted files

@@              Coverage Diff               @@
##           stable/bobcat     #624   +/-   ##
==============================================
  Coverage          89.41%   89.41%           
==============================================
  Files                 44       44           
  Lines               4686     4686           
==============================================
  Hits                4190     4190           
  Misses               496      496           

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[freyes]

This is fixing the build via updating the requirements.txt only, on that basis I'm merging with a single +2 to unblock the gate.