[FIX] portal: Fix broken repeated icon on portal attachment

Currently, when attachment small icon was displayed on portal it
is broken and repeated on background more than once like: task
attachment icon.

So in this commit do not repeat the icon when icon is small on portal
attachment.

closes odoo/odoo#61906

Taskid: 2337684
X-original-commit: 24304608
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/portal/static/src/scss/portal.scss

@@ -395,6 +395,7 @@ img, .media_iframe_video, .o_image {
 .oe_attachments .o_image_small {
     height: 40px;
     width: 50px;
+    background-repeat: no-repeat;
 }
 
 form label {