ubuntu 16.04 reached EoL, therefore switch github action to ubuntu 18.04 in that case

[daniel-mohr]

Since ubuntu 16.04 reached EoL (see actions/virtual-environments#3287), we have to switch the github action run-test-suite.yml to ubuntu 18.04.

[daniel-mohr]

Due to a change in the ubuntu github action (see actions/virtual-environments#4136) we need to do a apt-get update before installing packages sometimes. To not run in this problem once, I added this to run-test-suite_ubuntu_default_packages.yml.

[codecov-commenter]

Codecov Report

Merging #38 (574efd5) into master (0bd0e4d) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 574efd5 differs from pull request most recent head b28c2e0. Consider uploading reports for the commit b28c2e0 to get more accurate results

@@           Coverage Diff           @@
##           master      #38   +/-   ##
=======================================
  Coverage   81.10%   81.10%           
=======================================
  Files           2        2           
  Lines         677      677           
=======================================
  Hits          549      549           
  Misses        128      128           

Flag	Coverage Δ
unittests	81.10% <ø> (ø)

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[sadielbartholomew]

Thanks again @daniel-mohr. We'll get this PR, along with your other one open for cfunits, reviewed early next week.

[daniel-mohr]

@sadielbartholomew It's OK.

Development speed of your project is yours! ;-)

Thanks for accepting my work!