[LegacyCard] overflow hidden to protect border radius

Author: mattkubej

.changeset/clean-jobs-hear.md

@@ -0,0 +1,5 @@
+---
+'@shopify/polaris': patch
+---
+
+Protect border radius of `LegacyCard` with overflow hidden

polaris-react/src/components/LegacyCard/LegacyCard.scss

@@ -4,6 +4,7 @@
   background-color: var(--p-color-bg);
   box-shadow: var(--p-shadow-md);
   outline: var(--p-border-width-1) solid transparent;
+  overflow: hidden;
 
   + .LegacyCard {
     margin-top: var(--p-space-4);