[FIX] mail: add missing file to mail.assets_discuss_public

Add missing SCSS file to the assets bundle mail.assets_discuss_public
fixing issue with style that wasn't applied.

closes odoo/odoo#90106

X-original-commit: 001adac19e2e99373d3b8f52376a3361b462f082
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/__manifest__.py

@@ -68,6 +68,7 @@
             'web/static/lib/bootstrap/scss/_variables.scss',
             'web/static/src/legacy/scss/import_bootstrap.scss',
             'web/static/src/legacy/scss/bootstrap_review.scss',
+            'web/static/src/libs/bs5_utility_classes.scss',
             'web/static/src/webclient/webclient.scss',
             'web/static/src/webclient/webclient_extra.scss',
             'web/static/src/core/utils/*.scss',