unlock: Don't show prompt on shifty key presses

Shift, caps-lock and friends change the capitalization of following
key presses. It is unexpected for those keys to have side-effects,
so don't switch to the prompt when they are pressed.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/2215

js/ui/unlockDialog.js

@@ -593,6 +593,13 @@ var UnlockDialog = GObject.registerClass({
             (this._promptBox && this._promptBox.visible))
             return Clutter.EVENT_PROPAGATE;
 
+        const { keyval } = keyEvent;
+        if (keyval === Clutter.KEY_Shift_L ||
+            keyval === Clutter.KEY_Shift_R ||
+            keyval === Clutter.KEY_Shift_Lock ||
+            keyval === Clutter.KEY_Caps_Lock)
+            return Clutter.EVENT_PROPAGATE;
+
         let unichar = keyEvent.unicode_value;
 
         this._showPrompt();