[backend] Fix inject content when create simulation from scenario

[RomuDeuxfois]

Related issues

• Scenario with filled email create simulation without email content #1286

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 28.67%. Comparing base (fc98339) to head (0dbeea9).
Report is 6 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1293      +/-   ##
============================================
- Coverage     28.78%   28.67%   -0.11%     
- Complexity     1286     1295       +9     
============================================
  Files           507      507              
  Lines         13007    13222     +215     
  Branches        736      769      +33     
============================================
+ Hits           3744     3792      +48     
- Misses         9105     9271     +166     
- Partials        158      159       +1     

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