[backend/frontend] Fix removing a team from the context doesn't work

[RomuDeuxfois]

Closes #1521

Proposed changes

Related issues

• Removing a team from the context doesn't work #1521

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[codecov]

Codecov Report

Attention: Patch coverage is 76.47059% with 4 lines in your changes missing coverage. Please review.

Project coverage is 33.32%. Comparing base (9274617) to head (7408aab).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...openbas/rest/exercise/service/ExerciseService.java	75.00%	2 Missing and 1 partial ⚠️
...ain/java/io/openbas/rest/exercise/ExerciseApi.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1544      +/-   ##
============================================
+ Coverage     33.28%   33.32%   +0.04%     
  Complexity     1605     1605              
============================================
  Files           557      557              
  Lines         14474    14476       +2     
  Branches        871      871              
============================================
+ Hits           4817     4824       +7     
+ Misses         9435     9431       -4     
+ Partials        222      221       -1     

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[RomuDeuxfois]

Need to be retest by me before review

[RomuDeuxfois]

All good :)
Ready for a second round