assert_fs belongs in dev-dependencies

[pocopepe]

Closes #323
A simple move to fix the wasm build

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.25%. Comparing base (7b204c0) to head (fe411ec).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #379   +/-   ##
=======================================
  Coverage   82.25%   82.25%           
=======================================
  Files          13       13           
  Lines        5438     5438           
  Branches      304      304           
=======================================
  Hits         4473     4473           
  Misses        963      963           
  Partials        2        2           

Flag	Coverage Δ
macos_latest	82.70% <ø> (ø)
ubuntu_latest	82.81% <ø> (ø)
windows_latest	0.00% <ø> (ø)

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[cakebaker]

Good catch, thanks!