iox-#1906 Use Ubuntu 20 for ROS GitHub action

[dkroenke]

Pre-Review Checklist for the PR Author

1. Code follows the coding style of CONTRIBUTING.md
2. Tests follow the best practice for testing
3. Changelog updated in the unreleased section including API breaking changes
4. Branch follows the naming format (iox-123-this-is-a-branch)
5. Commits messages are according to this guideline
   • Commit messages have the issue ID (iox-#123 commit text)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
6. Update the PR title
   • Follow the same conventions as for commit messages
   • Link to the relevant issue
7. Relevant issues are linked
8. Add sensible notes for the reviewer
9. All checks have passed (except task-list-completed)
10. All touched (C/C++) source code files from iceoryx_hoofs are added to ./clang-tidy-diff-scans.txt
11. Assign PR to reviewer

Notes for Reviewer

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Code according to our coding style and naming conventions
• Unit tests have been written for new behavior
• Public API changes are documented via doxygen
• Copyright owner are updated in the changed files
• All touched (C/C++) source code files from iceoryx_hoofs have been added to ./clang-tidy-diff-scans.txt
• PR title describes the changes

Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

References

• Closes TBD

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This change is 

[codecov-commenter]

Codecov Report

Merging #33 (d278407) into master (0487837) will increase coverage by 0.00%.
The diff coverage is n/a.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #33   +/-   ##
=======================================
  Coverage   75.45%   75.45%           
=======================================
  Files         383      383           
  Lines       15178    15178           
  Branches     2148     2148           
=======================================
+ Hits        11452    11453    +1     
  Misses       3055     3055           
+ Partials      671      670    -1     

Flag	Coverage Δ
unittests	75.11% <ø> (+<0.01%)	⬆️
unittests_timing	15.47% <ø> (ø)

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

Impacted Files	Coverage Δ
iceoryx_hoofs/source/concurrent/loffli.cpp	90.90% <0.00%> (+3.03%)	⬆️