fix: show meetecho recordings for groups with more than one session

[rjsparks]

Fixes #8236

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.94%. Comparing base (c7f6bde) to head (031e000).
Report is 191 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8238      +/-   ##
==========================================
+ Coverage   88.78%   88.94%   +0.15%     
==========================================
  Files         296      303       +7     
  Lines       41320    41282      -38     
==========================================
+ Hits        36687    36718      +31     
+ Misses       4633     4564      -69     

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[jennifer-richards]

lgtm. The only fault I see is the very opaque way that _format_materials() filters out non-Truthy materials, but that's for another day...