Lua 5.5 incompatibility

[SeseMueller]

Lua 5.5 was released in December of 2025, and one of the changes was that variables from a for loop are now const. See https://www.lua.org/manual/5.5/readme.html#Main%20changes

This breaks Ipe because in the main.lua file, the variable from a for loop is mutated:

ipe/src/ipe/lua/main.lua

Lines 392 to 393 in d948b7e

	for w in string.gmatch(ipestyles, prefs.fname_pattern) do
	if w == "_" then w = ipe.folder("styles") end

Downgrading to Lua 5.4 finally allowed me to compile Ipe.