fix(nix-monitor): fix some warnings

nix-monitor/nix_monitor.luau

@@ -11,16 +11,14 @@ function getState(key)
 end
 
 function displayWidget(glyph: string, text: string, color: string?)
-    if color == nil then
-        color = "on_surface"
-    end
+    local _color = color or "on_surface"
 
     if cfg("colorize_text") then
-        barWidget.setColor(color)
+        barWidget.setColor(_color)
     end
 
     if cfg("colorize_glyph") then
-        barWidget.setGlyphColor(color)
+        barWidget.setGlyphColor(_color)
     end
 
     if cfg("show_glyph") then

nix-monitor/panel.luau

@@ -234,7 +234,7 @@ function onCancelClicked()
 end
 
 function onUpdateClicked()
-    command = cfg("update_command")
+    local command = cfg("update_command")
     if command == "" then
         noctalia.notifyError(tr("notification.update_command_is_empty"))
         return
@@ -249,7 +249,7 @@ function onUpdateClicked()
 end
 
 function onCleanClicked()
-    command = cfg("clean_command")
+    local command = cfg("clean_command")
     if command == "" then
         noctalia.notifyError(tr("notification.clean_command_is_empty"))
         return