layouts: Fill some placeholders with '²' and '³'

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/703>

data/keyboards/th.yaml

@@ -26,13 +26,13 @@ views:
         - "show_upper ( ) ฉ ฮ ฺ ์ ? ฒ ฬ ฦ BackSpace"
         - "show_numbers preferences space .-large Return"
     numbers:
-        - "-- -- -- -- -- -- -- -- -- -- -- --"
+        - "-- -- -- -- -- -- -- -- -- -- ² ³"
         - "1 2 3 4 5 6 7 8 9 0"
         - "@ # $ % & - _ + ( )"
         - "show_symbols , \" ' : ; ! ? BackSpace"
         - "show_letters preferences space .-large Return"
     symbols:
-        - "-- -- -- -- -- -- -- -- -- -- -- --"
+        - "-- -- -- -- -- -- -- -- -- -- ² ³"
         - "© ® £ € ¥ ^ ° * { }"
         - "~ ` | · √ π τ ÷ × ¶"
         - "show_numbers_from_symbols \\ / < > = [ ] BackSpace"