Fix CI

lua.org has been down all day, so CI has been dead. This switches to using the GitLab-hosted archives I just uploaded here instead: openmw-deps@9b00c68f. There's an incredibly slim chance that this isn't the right file as it came from The Wayback Machine as lua.org's been down all day. Closes #8031 (closed).

Also, CI was broken before lua.org went down this morning as the MR to bump the Qt version (and therefore the cache key) was merged, and that means the job takes about twenty more minutes than normal until the cache is initialised. I don't understand how we avoided this problem the last time we bumped the Qt version - nominally, protected branches (which for us is just master) have separate cache, so any hoop-jumping we do in MRs shouldn't end up avoiding this after those MRs are merged. To avoid having hacks like a series of builds that only build part of the project and the related commits and broken dev builds that would cause, I've added a job with a manual trigger that will initialise the dependency cache when it's run by not actually building anything. The cache key's shared with the regular job, so it'll then unbreak things. This is what the button looks like: