Convert Travis tests to GitHub actions

[duboism]

Travis no longer gives free access to free projects. Therefore, this PR converts the test suite to GitHub actions.

Technical details

Here are a few notes:

• The test suite itself is not changed. It still work from 5.6 to 7.4
• We use Setup PHP Action to set up PHP.
• pear must be run with sudo. Therefore, for now, we test only on Ubuntu and macOS because there is no sudo on Windows.
• The action is configured to run on pull requests and when pushing on certain branches.
• The action can be launched manually from GitHub interface (at least from @duboism/HTML_Template_IT): go in the Actions tab, select Main on the left and in the drop box, select branch github_actions_master and then click the Run workflow button.

Relation to #15 and #17

As of 2186e20, #15 is a bit buggy (conflicts in versions of PHPUnit).

This PR was developed to simplify the development of #15 but since then I found a better approach to modernize the test suite which is in #17.

#17 is based on this branch so merging this would greatly help.

[Neustradamus]

@duboism: Good job!

[duboism]

@duboism: Good job!

Just to know: did you try to run the actions ?

[duboism]

While paying a bit more attention to the test output, I noticed that PHPUnit warns about some deprecated code (namely, the dynamic creation of a property which is deprecated since PHP 8.2). I will address that in another PR.

There is another deprecation: the XML configuration file for PHPUnit changed in version 10. I guess this should be addressed at some point too.

[duboism]

@pear ?

[duboism]

By the way, I realized that some pear packages (like pear/pear-core) already moved to GitHub actions. AFAICS, the actions are similar to what I propose here but if somebody knows better, don't hesitate.

[duboism]

There is another deprecation: the XML configuration file for PHPUnit changed in version 10. I guess this should be addressed at some point too.

I removed the configuration file and updated the actions.

[duboism]

Thank you @ashnazg !

[Neustradamus]

Thanks to @duboism for this PR and @ashnazg for merging!
Good job!

Can you add "Issues" section?