Update GNOME lock screen needle

Seems they changed it from the user's initials to a generic icon.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

needles/gnome/apps/gnome-panel/panel_screen_locked-20240419.json

@@ -0,0 +1,15 @@
+{
+  "area": [
+    {
+      "width": 90,
+      "xpos": 467,
+      "ypos": 286,
+      "type": "match",
+      "height": 104
+    }
+  ],
+  "properties": [],
+  "tags": [
+    "panel_screen_locked"
+  ]
+}