[CI] allow `luarocks config --user-config` to fail

tests/runci/targets/Lua.hx

@@ -60,7 +60,7 @@ class Lua {
 			runCommand("luarocks", ["config", "--lua-libdir"]);
 			runCommand("luarocks", ["config", "--lua-ver"]);
 			runCommand("luarocks", ["config", "--system-config"]);
-			runCommand("luarocks", ["config", "--user-config"]);
+			runCommand("luarocks", ["config", "--user-config"], false, true); //can fail when there is no user config
 			runCommand("luarocks", ["config", "--rock-trees"]);
 
 			installLuaVersionDependencies(lv);