[FIX] account: dashboard: Center the empty dashboard message horizontally when the setup bar is displayed on a small screen

Before that, when using a small screen (with width <= 768 px) and
showing the accounting dashboard of a company without any chart of
accounts installed, the icon and message prompting to install a chart of
accounts was displayed in the lower left corner, instead of being
horizontally centered.

closes odoo/odoo#36974

X-original-commit: 4999f47d7e283c6a5799e68f2b0e1351638e17a3
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>
Co-authored-by: Nicolas Lempereur <nle-odoo@users.noreply.github.com>

addons/web/static/src/scss/banner.scss

@@ -1,8 +1,9 @@
 .o_has_banner {
     .o_view_nocontent {
         top: 30%;
-        @media screen and (max-height:  map-get($grid-breakpoints, 'md')) {
+        @include media-breakpoint-down(sm) {
             position: relative;
+            margin: auto;
         }
     }
 }