tests: migrate from Travis to GitHub Actions

[DeepDiver1975]

Run phpunit on php 7.1 - 8.1 and partially runs cs-fixer and phpstan
Coverage is uploaded to codecov.

[codecov]

Codecov Report

Merging #206 (d102a62) into master (3133060) will decrease coverage by 0.33%.
The diff coverage is n/a.

❗ Current head d102a62 differs from pull request most recent head 24043b9. Consider uploading reports for the commit 24043b9 to get more accurate results

@@             Coverage Diff              @@
##             master     #206      +/-   ##
============================================
- Coverage     97.62%   97.29%   -0.34%     
- Complexity      114      116       +2     
============================================
  Files            13       13              
  Lines           464      481      +17     
============================================
+ Hits            453      468      +15     
- Misses           11       13       +2     

Impacted Files	Coverage Δ
lib/Serializer/functions.php	97.95% <0.00%> (-2.05%)	⬇️
lib/Service.php	98.50% <0.00%> (-1.50%)	⬇️
lib/Writer.php	100.00% <0.00%> (ø)
lib/Element/Uri.php	100.00% <0.00%> (ø)
lib/Element/Base.php	100.00% <0.00%> (ø)
lib/Element/Cdata.php	100.00% <0.00%> (ø)
lib/LibXMLException.php	100.00% <0.00%> (ø)
lib/Element/Elements.php	100.00% <0.00%> (ø)
lib/Element/KeyValue.php	100.00% <0.00%> (ø)
lib/ContextStackTrait.php	100.00% <0.00%> (ø)
... and 1 more

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[phil-davis]

@DeepDiver1975 - one of our guys, @kiranparajuli589 would like to practice setting up GitHub actions. So I could allocate a repo for him to do, and then when that is done he/others could do more of them.

[DeepDiver1975]

@DeepDiver1975 - one of our guys, @kiranparajuli589 would like to practice setting up GitHub actions. So I could allocate a repo for him to do, and then when that is done he/others could do more of them.

Fine for me .... but it will only be copying the workflow file to other repos ;-)
Anyway - go ahead - THX

[phil-davis]

but it will only be copying the workflow file to other repos

It will be mostly copy-paste-minor-edit, but he will find out if there are "bonus tricks" in other repos.