fix(NcModal): use --border-radius-container

> Currently, the border radius is quite low and eg. the close button doesn't nest nicely within it.
> If I see it correctly, with 4px of padding around it, the outer radius should be 12px (8+4).

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

src/components/NcModal/NcModal.vue

@@ -1062,7 +1062,7 @@ export default {
 		display: flex;
 		padding: 0;
 		transition: transform 300ms ease;
-		border-radius: var(--border-radius-large);
+		border-radius: var(--border-radius-container, var(--border-radius-rounded));
 		background-color: var(--color-main-background);
 		color: var(--color-main-text);
 		box-shadow: 0 0 40px rgba(0, 0, 0, .2);