chore: clarify Lua submodule version

[brian6932]

Updating submodules causes

lib\sol2\include\sol/compatibility/compat-5.3.h(404): fatal error C1189: #error: "unsupported Lua version (i.e. not Lua 5.1, 5.2, 5.3, or 5.4)"

• sol requires 501-504
  https://github.com/ThePhD/sol2/blob/2b0d2fe8ba0074e16b499940c4f3126b9c7d3471/include/sol/compatibility/compat-5.3.h#L401-L406
• lua master uses 505
  https://github.com/lua/lua/blob/e3ce88c9e850b7e79751083014699c5eae1bff31/lua.h#L20-L24

[Nerixyz]

lua master uses 505

That shouldn't matter. We're checked out on the v5.4.7 tag. If we'd use the latest master commit, Sol would break in CI.

[brian6932]

We're checked out on the v5.4.7 tag

Yes, but it's not exactly clear that updating submodules will break the build. Imo the branch should just be specified in .gitmodules, especially since lua releases are set to their own branches anyway.

[pajlada]

This is less of a fix, and more of a hint to future developers clarifying what branch we're tracking.
It also makes it easier for us to be able to track changes to that specific branch, since Lua maintains old versions as branches