Before this commit, the popover containing the volume bar of the rtc call participant card was rendered empty. This was because the `t-set` was used instead of `t-set-slot`. This commit fixes this issue. related to: https://github.com/odoo/odoo/commit/edd79ff560cf321ebd0488e4917abb7424fea1bb closes odoo/odoo#85106 Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>