Fix spawner tests timeout on source builds (backport #1692)

[mergify]

As reported by @christophfroehlich in #1685, it seems that spawner tests are inconsistent and timing out after some time. I was able to reproduce it locally and upon checking it seems like the CM's internal mutexes are blcoking as there is no ControllerManagerRunner in some of these tests. Adding these should fix the above timeout issues. I've tested it locally and it seems to work

Fixes #1685

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This is an automatic backport of pull request #1692 done by Mergify.

[mergify]

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	both modified:   controller_manager/test/test_spawner_unspawner.cpp

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.17%. Comparing base (c2760b4) to head (30d8608).
Report is 10 commits behind head on iron.

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1698      +/-   ##
==========================================
- Coverage   62.17%   62.17%   -0.01%     
==========================================
  Files         109      109              
  Lines       12205    12210       +5     
  Branches     8551     8556       +5     
==========================================
+ Hits         7589     7591       +2     
- Misses        867      868       +1     
- Partials     3749     3751       +2     

Flag	Coverage Δ
unittests	62.17% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
controller_manager/test/test_spawner_unspawner.cpp	58.25% <100.00%> (+0.52%)	⬆️

... and 2 files with indirect coverage changes