Changes implicitly nullable to explicitly nullable

[LukeWCS]

Fixes #122

[iMattPro]

What happens if you add - php: '8.4' to the test.yml too, to see how EPVs tests go here in 8.4?

[LukeWCS]

What happens if you add - php: '8.4' to the test.yml too, to see how EPVs tests go here in 8.4?

I haven't tested this because I use phpBB Ext Check. This means I'm essentially working with a standalone installation of EPV.

The most I could do is test it with my test repo and set up the phpBB GH Actions framework there. But even if no DEPRECATED messages appear there, that doesn't help me because I need EPV for phpBB Ext Check.

[iMattPro]

I meant just set it here as part of this PR and let's see if they pass too. If not, remove it.

[LukeWCS]

Ah, I think I understand now. FYI: I have little knowledge of GitHub and none at all of GH Actions or Unit Tests. ^^

Testing...