[FIX] website_event: display a good resolution of thumbnails on event cards

Steps:
- Go to website and edit
- Add an event block
- Change the template of the block from picture to card layout.
- Replace the image of one card by a 4k image.

Issue:
The custom cover is blurry.

Reason:
By default the custom cover is resized to 256x256 (but not the default one because
it uses a static image path).

opw-3390459

closes odoo/odoo#152278

X-original-commit: d6d24ceb2a5b6e735ffb2fe1d5cea1f8f945f288
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>
Signed-off-by: Jérémy Hennecart (jeh) <jeh@odoo.com>

addons/website_event/views/snippets/s_events.xml

@@ -46,8 +46,8 @@
             <a class="s_events_event_cover" t-att-href="data['call_to_action_url']">
                 <t t-call="website.record_cover">
                     <t t-set="_record" t-value="record"/>
-                    <t t-set="_resize_height" t-value="256"/>
-                    <t t-set="_resize_width" t-value="256"/>
+                    <t t-set="_resize_height" t-value="512"/>
+                    <t t-set="_resize_width" t-value="512"/>
 
                     <div class="s_events_event_date position-absolute shadow-sm text-dark">
                         <span t-field="record.date_begin" t-options="{'format': 'LLL', 'tz_name': record.date_tz}"