I have found a bug in Lua 5.4.2.
The value of math.mininteger is the integer -9223372036854775808.
If you were to write the number itself, instead of accessing it through the math.mininteger constant, the Lua parser would instead produce the float -9.2233720368548e+18
This occurs both on the REPL, as well as when loading a Lua file.
Funny enough the value just next to math.mininteger, which is to say -9223372036854775807, correctly parses into an integer instead of a float. So it seems only math.mininteger suffers this bug. The value of math.maxinteger also correctly parses into an integer.
I can work around this bug, but I hope it's chosen to be fixed.