TOOLS/observe-all.lua: fix lint warning

.luacheckrc

@@ -110,7 +110,6 @@ max_line_length = 100
 -- TODO: Remove everything below this line
 local todo = {
     "player/lua/osc.lua",
-    "TOOLS/lua/observe-all.lua",
     "TOOLS/lua/osd-test.lua",
     "TOOLS/lua/status-line.lua",
     "TOOLS/lua/test-hooks.lua",

TOOLS/lua/observe-all.lua

@@ -6,7 +6,7 @@
 
 local utils = require("mp.utils")
 
-function observe(name)
+local function observe(name)
     mp.observe_property(name, "native", function(prop, val)
         print("property '" .. prop .. "' changed to '" ..
               utils.to_string(val) .. "'")