textview: raise a bit magnifier popover

Not a good hint if the finger covers bits of the magnifier itself, this
seems enough to at least only cover the tail.

gtk/gtktextview.c

@@ -4746,8 +4746,8 @@ gtk_text_view_show_magnifier (GtkTextView *text_view,
   _gtk_magnifier_set_coords (GTK_MAGNIFIER (priv->magnifier),
                              rect.x, rect.y + rect.height / 2);
 
-  rect.height /= 2;
-  rect.y += rect.height;
+  rect.y += rect.height / 4;
+  rect.height -= rect.height / 4;
   gtk_popover_set_pointing_to (GTK_POPOVER (priv->magnifier_popover),
                                &rect);