Add Lua 5.4 to test matrices

[alerque]

No description provided.

[alerque]

I've opened an upstream report about luacheck, but at the same time I'm pretty sure that doesn't need to get run for every Lua version in the matrix, it only needs to be run once.

[alerque]

The error thrown by the test suite here does not seem to be the same as the one shown in #320. Apparently there is more to fix ... and I'm guessing the test runner order may be non-deterministic.

@mcepl Did you get past the rest of the test suite after patching that one issue?

[mcepl]

@mcepl Did you get past the rest of the test suite after patching that one issue?

I do believe so. See https://build.opensuse.org/package/show/devel:languages:lua/lua-penlight (click on the “succeed” links to see the build logs), or this build log (search for %check string to find the beginning of the testing phase).