[FIX] hr_expense: css issue on attachment

Before this pr, when attaching an image to an expense, the image was misplaced.
By adding a display flex and justify the content in the center, the image is now
vertically align in the center.

closes odoo/odoo#121607

Task-id: 3329707
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/hr_expense/static/src/scss/hr_expense.scss

@@ -19,6 +19,12 @@
     }
 }
 
+.o_center_attachment .o-mail-Attachment-imgContainer {
+    display: flex;
+    justify-content: center;
+    z-index: -1;
+}
+
 .o_dropzone {
     width: 100%;
     height: 100%;

addons/hr_expense/views/hr_expense_views.xml

@@ -215,7 +215,7 @@
                         <field name="description" placeholder="Notes..."/>
                     </div>
                 </sheet>
-                <div class="o_attachment_preview"/>
+                <div class="o_attachment_preview o_center_attachment"/>
                 <div class="oe_chatter">
                     <field name="message_follower_ids"/>
                     <field name="activity_ids"/>