[FIX] web: fix border radius of buttons within input-group

Since the commit [1] introducing Bootstrap 5, buttons within input
groups (e.g., "search bars") no longer have the same border-radius as
the inputs.

Steps to reproduce the bug:
- In Website edit mode, drag and drop a "Search" snippet onto the page.
- Click on the "Theme" tab.
- Set the inputs "Border Radius" option to 25px.
- Bug: The border-radius is not applied to the right side of the search
bar.

[1]: https://github.com/odoo/odoo/commit/9ea13513342b14e6b8d4e10e162b618a6ab2cce0

task-3662985

closes odoo/odoo#156603

X-original-commit: 58b57af056a83cda3d8caa6c22d8564c3f9816c9
Signed-off-by: Soukéina Bojabza (sobo) <sobo@odoo.com>

addons/web/static/src/scss/bootstrap_review_frontend.scss

@@ -219,3 +219,10 @@ $-color-for-gray-200-bg: adjust-color-to-background($body-color, $gray-200);
         }
     }
 }
+
+// Button within input-group (e.g., "search bar")
+.input-group {
+    .btn:first-child, .btn:last-child {
+        @include border-radius($input-border-radius, 0);
+    }
+}