Run AllTests on PHP8 #16897

Description:

Runs AllTests on PHP 8 instead of PHP 7.4

Review

• [ ] Functional review done
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done see checklist
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

@tsteur the tests are running now on PHP 8. But I needed to update to PHPUnit 9 for that build, as PHPUnit 8.5 doesn't support PHP 8. Unfortunately PHPUnit 9 doesn't support PHP < 7.3, so we can't update in general.

Nevertheless there seem a lot tests failing. Would need some time to investigate that a bit further. Let me know if or when I should plan to do that.

@sgiehl it seems to be mostly working? we could look into it as part of 4.1 if it's somewhat quick to do to fix these issues.

For now priority is 4.0.X and I think I pinged you on few other sec issues etc

@tsteur Actually might be a bit more. The second build that is shown as success actually silently fails. See https://travis-ci.com/github/matomo-org/matomo/jobs/455444024#L996
Not yet sure why the tests suddenly abort while running.

Some tests are failing due to adjustments required in TCPDF. Those should be fixed with https://github.com/tecnickcom/TCPDF/pull/293
Waiting for a new release to get that fixed...

@sgiehl I just saw that there were a few TCPDF releases last week:
https://github.com/tecnickcom/TCPDF/releases

@Findus23 correct. But the main branch still contains some extra fixes for php 8. See https://github.com/tecnickcom/TCPDF/compare/6.3.5...main

:facepalm: Okay, that was my mistake. I saw 14 Feb and totally missed that it was 2020 and not 2021.
So it seems like the status continues that there is no release including the PHP 8 fixes.

Is this PR just for modifying the PHP8 version on travis or we want to do the same for local development?
If we want to make it work locally, we have to update phpunit in the composer.json as well.

And there is one more small issue running the test locally on PHP8:
Before we run the tests we have to migrate the tests db, by running ./console tests:setup-fixture OmniFixture. But during this process there is an issue on PHP8 in tests/PHPUnit/Fixtures/InvalidVisits.php file, because the json_decode throws a TypeError instead of Exception.

If this PR is for running the tests locally on PHP8 as well, we need to make those modifications.

@flamisz We can't update PHPUnit locally as the latest version doesn't run on PHP 7.2. But the currently used version doesn't work with PHP 8. So we actually need to wait until our requirement was raised to PHP 7.3, so we can use PHPUnit 9 globally.

For now this PR was only meant to run travis tests on PHP 8