Pin snmpsim to older version

[stveit]

same issue as we had for Zino

A new version of snmpsim was released about 6 hours ago (the first new version in 5 years), and it seems to have changed to be incompatible with how our test suite uses it.

In particular, our test suite expects snmpsimd.py to be available on the search PATH, but the executable's name may have changed, and I don't have the luxury of time to figure out how to adapt our test suite

I assume there may be many more changes, as the original maintainer died a while back, and someone else has taken over, which is why I think it's best to pin to an older version for now.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.35%. Comparing base (b8d6d52) to head (b5a98ce).
Report is 380 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2946   +/-   ##
=======================================
  Coverage   56.35%   56.35%           
=======================================
  Files         603      603           
  Lines       43862    43862           
  Branches       48       48           
=======================================
  Hits        24719    24719           
  Misses      19131    19131           
  Partials       12       12           

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