Bug 42236: Add accessible label to OPAC user lists actions column

To recreate:
1. Log in to the OPAC
2. Create at least 1 list
3. Go to the "Your lists" page (opac-userlists)
4. Inspect the table header for the Edit/Delete column
5. Confirm the header contains no text

Test the patch:
1. Apply the patch
2. Repeat steps 1-3
3. Inspect the table header for the Edit/Delete column
4. Confirm the header now contains accessible text
5. Confirm Edit and Delete actions still function as expected
6. Run an accessibility checker and confirm the issue is resolved
7. Sign off and have a wonderful day! :D

Signed-off-by: John Vinke <jvinke@austinseminary.edu>
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 88676495e0)
Signed-off-by: Jacob O'Mara <Jacob.omara@openfifth.co.uk>
Signed-off-by: Wainui Witika-Park <wainuiwitikapark@catalyst.net.nz>

koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-shelves.tt

@@ -720,7 +720,7 @@
                                                 <th>Contents</th>
                                                 <th>Type</th>
                                                 <th>Modification date</th>
-                                                <th>&nbsp;</th>
+                                                <th>Actions</th>
                                             </tr>
                                         </thead>
                                         <tbody>