Change label of "PgUp" and "PgDn", to "Page ↑" and "Page ↓"

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/625>

data/keyboards/terminal/us.yaml

@@ -18,7 +18,7 @@ views:
         - "Shift_L   z x c v b n m  BackSpace"
         - "show_numbers preferences      space        show_actions Return"
     upper:
-        - "TabSmall Ctrl Alt PgUp PgDn Home End"
+        - "TabSmall Ctrl Alt PageUp PageDown Home End"
         - "Q W E R T Y U I O P"
         - "SlashSmall A S D F G H J K L PipeSmall"
         - "Shift_L   Z X C V B N M  BackSpace"
@@ -36,7 +36,7 @@ views:
         - "show_numbers_from_symbols   % | < > = [ ]  BackSpace"
         - "show_letters preferences         space        period Return"
     actions:
-        - "TabSmall Ctrl Alt PgUp PgDn Home End"
+        - "TabSmall Ctrl Alt PageUp PageDown Home End"
         - "F1  F2  F3  F4  F5  F6"
         - "F7  F8  F9  F10 F11 F12"
         - "Esc Tab Pause Insert Up Del"
@@ -167,12 +167,14 @@ buttons:
     End:
         outline: "small"
         keysym: "End"
-    PgUp:
+    PageUp:
         outline: "small"
         keysym: "Page_Up"
-    PgDn:
+        label: "Page ↑"
+    PageDown:
         outline: "small"
         keysym: "Page_Down"
+        label: "Page ↓"
     "↑":
         outline: "small"
         keysym: "Up"