Only yield msgs with valid msg types in generate_messages

[paulovcmedeiros]

• [x] Tests added
• [x] Tests passed
• [x] Passes flake8 trollflow2
• [x] Add your name to AUTHORS.md if not there already

[codecov[bot]]

Codecov Report

Merging #172 (e2a1f27) into main (47986eb) will increase coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #172      +/-   ##
==========================================
+ Coverage   95.66%   95.69%   +0.02%     
==========================================
  Files          11       11              
  Lines        2470     2485      +15     
==========================================
+ Hits         2363     2378      +15     
  Misses        107      107              

Flag	Coverage Δ
unittests	95.69% <100.00%> (+0.02%)	:arrow_up:

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

Impacted Files	Coverage Δ
trollflow2/launcher.py	87.83% <100.00%> (+0.12%)	:arrow_up:
trollflow2/tests/test_launcher.py	98.12% <100.00%> (+0.05%)	:arrow_up:

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