[FIX] website: fix image gallery arrows hidden after click

Steps to reproduce the bug:

- Drag and drop an Image Gallery Snippet onto the page.
- Add an image in the Gallery.
- Click on the "right" arrows.
- The arrow is gone.

A bug similar to this one had already been fixed by the commit [1] that
added the "o_not_editable" class to the "carousel-control" elements of
the "s_image_gallery" snippet. However, it was also necessary to make
this change in the QWeb template used when the slideshow is regenerated
upon adding an image.

[1]: https://github.com/odoo/odoo/commit/ef7adab23b310001ea8f7ff8cd304b11a5464c7d

task-3414584

closes odoo/odoo#128133

X-original-commit: 0983553f4df2b027290082c03142db4bfb5f288c
Signed-off-by: Colin Louis (loco) <loco@odoo.com>
Signed-off-by: Benjamin Vray (bvr) <bvr@odoo.com>

addons/website/static/src/snippets/s_image_gallery/000.xml

@@ -31,11 +31,11 @@
                 </li>
             </ul>
 
-            <a class="carousel-control-prev o_we_no_overlay" t-attf-href="##{id}" data-bs-slide="prev" aria-label="Previous" title="Previous">
+            <a class="carousel-control-prev o_we_no_overlay o_not_editable" t-attf-href="##{id}" data-bs-slide="prev" aria-label="Previous" title="Previous">
                 <span class="oi oi-chevron-left fa-2x text-white"></span>
                 <span class="visually-hidden">Previous</span>
             </a>
-            <a class="carousel-control-next o_we_no_overlay" t-attf-href="##{id}" data-bs-slide="next" aria-label="Next" title="Next">
+            <a class="carousel-control-next o_we_no_overlay o_not_editable" t-attf-href="##{id}" data-bs-slide="next" aria-label="Next" title="Next">
                 <span class="oi oi-chevron-right fa-2x text-white"></span>
                 <span class="visually-hidden">Next</span>
             </a>