Fix debug information about finalizers

The flag CIST_FIN does not mark a finalizer, but the function that was
running when the finalizer was called. (So, the function did not call
the finalizer, but it looks that way in the stack.)

testes/db.lua

@@ -887,7 +887,7 @@ do   -- testing debug info for finalizers
 
   -- create a piece of garbage with a finalizer
   setmetatable({}, {__gc = function ()
-    local t = debug.getinfo(2)   -- get callee information
+    local t = debug.getinfo(1)   -- get function information
     assert(t.namewhat == "metamethod")
     name = t.name
   end})