views/agenda-view-day-row: Adjust focusability of row and event widget

For unknown reasons, the `::row-activated` signal is not emitted
whenever the user presses an activation button on the keyboard
such as Enter or Space, even though the list box row has focus.

Ideally, we want the list box rows to be activatable, so that
activating them will simply emit the "event-activated" signal and
pop up the popover.

Since this doesn't work, the next best thing is to make the event
widgets themselves focusable and the list box rows unfocusable.
This will unfortunately lose the ability to navigate with arrow
keys, as well as Home/End and Page Up/Down. However, the user will
at least be able to activate them and access events in
the agenda view.

A `FIXME` label has been added because this should be fixed as soon
as possible.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/807>

src/gui/views/gcal-agenda-view-day-row.c

@@ -144,12 +144,13 @@ create_day_row_func (gpointer item,
                          "event", event,
                          "orientation", GTK_ORIENTATION_VERTICAL,
                          "timestamp-policy", timestamp_policy,
-                         "focusable", FALSE,
                          NULL);
 
   row = g_object_new (GTK_TYPE_LIST_BOX_ROW,
                       "child", widget,
-                      "activatable", TRUE,
+                      /* FIXME: The event widget itself should be unfocusable, not this.
+                       *        More information in `git blame`. */
+                      "focusable", FALSE,
                       NULL);
 
   gtk_accessible_update_property (GTK_ACCESSIBLE (row),