Update MUI to v6

[piotrpospiech]

• Updated @mui/material to v6 in the uniforms-mui theme
• Updated @mui/material in the reproductions directory
• MUI v6 doesn't introduce breaking changes that has impact on our theme (MUI migration guide)
  • only breaking changes affecting testing (docs) could interfere with our tests, but I didn't notice any additional warnings

Screenshot (all fields example from playground)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.53%. Comparing base (bd93a0b) to head (5c0d824).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1381   +/-   ##
=======================================
  Coverage   95.53%   95.53%           
=======================================
  Files         175      175           
  Lines        2867     2867           
  Branches      774      774           
=======================================
  Hits         2739     2739           
  Misses         59       59           
  Partials       69       69           

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