Moodle 405 stable runtest fixes

[SashaAnastasi]

No description provided.

[SashaAnastasi]

This failure is caused by ACPu being assumed disabled in the runtest. ACPu is disabled on NZEL servers.
It wasn't failing before because the assertion, being placed after an expectException, wasn't actually running.
Suggested fix is to disable ACPu in the runtest container.

[Peterburnett]

It looks like we are still seeing CI failures here on the GA bots, likely due to some difference in containers or similar to do with APCu. My recommendation here is that we move the tests over to use 'file' instead of 'apcu' so the test environment is consistent everywhere, after which the tests should be green here. Functional change to the boolean logic looks good

[SashaAnastasi]

The suggestion makes sense. I'll add a commit to reflect this.

[danmarsden]

merging this in for now to get our tests passing... @Peterburnett feel free to add further commits on top if you want to see it implement some improvements to tests!