data/keyboards/*.yaml: Change "abc" to "ABC"

Currently this differs for the same view-change-keys in different layouts.

When the text is "abc", the size of the key's text changes
when toggling between "123" and "abc"; with the text "ABC",
the size remains about the same.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/611>

data/keyboards/bg.yaml

@@ -59,7 +59,7 @@ buttons:
         action:
             set_view: "base"
         outline: "wide"
-        label: "abc"
+        label: "ABC"
     show_symbols:
         action:
             set_view: "symbols"