Update for Moodle 5.0

[TamaroWalter]

This PR adapts the repo to the new changes of Moodle 5.0.

Changes made:

• update moodle ci to moodle 5.0

Todo's:

[bluetom]

This is the only reasonable way at the moment, I guess...?

[dlmsr]

I have rebased the changes onto main and re-arranged some commits. I
have also removed the allow-mustache-lint-error part which was
questioned by @bluetom. Then, I updated the thirdparty library
endroid/qr-code to the latest release 6.0.0. Let’s see what CI has to
say.

[dlmsr]

As discussed with @bluetom and @TamaroWalter I have removed two commits and pushed a v3 of this branch. We agreed on making the code checker ignore the thirdparty/ code since it violates Moodle coding standards anyway so there is no point in checking for it. @TamaroWalter will adapt the central Learnweb workflow files to make this work. Since we want to support 4.1 for a couple of weeks, we cannot upgrade the endroid/qr-code library to a newer version because the required PHP versions would be incompatible. We stick with the current 4.x version for now.

[dlmsr]

I have just noticed that the problems do not arise with the code checker. The vendor directories are excluded in MoodleHQ's PHPCodeSniffer standard anyways. The problems arise in the Behat and PHPUnit tests directly.