Also lock assert_cmd version

[shssoichiro]

This package also bumped their minimum rustc version in a patch version to one that we don't support.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.54%. Comparing base (3c3a26f) to head (2b8779b).
Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3358      +/-   ##
==========================================
+ Coverage   88.52%   88.54%   +0.01%     
==========================================
  Files          89       89              
  Lines       28323    28355      +32     
==========================================
+ Hits        25074    25107      +33     
+ Misses       3249     3248       -1     

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