Dockerfile: fix JSONArgsRecommended warning

[thaJeztah]

1 warning found (use docker --debug to expand):
- JSONArgsRecommended: JSON arguments recommended for CMD to prevent unintended behavior related to OS signals (line 120)

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.50%. Comparing base (ff5fdfa) to head (7b348e4).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5950      +/-   ##
==========================================
+ Coverage   59.47%   59.50%   +0.02%     
==========================================
  Files         357      357              
  Lines       29744    29744              
==========================================
+ Hits        17690    17698       +8     
+ Misses      11090    11081       -9     
- Partials      964      965       +1     

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