Fix centered modal scrolling issue (#30244)

Use the `min-content` property.

scss/_modal.scss

@@ -83,6 +83,7 @@
   &::before {
     display: block; // IE10
     height: subtract(100vh, $modal-dialog-margin * 2);
+    height: min-content; // Reset height to 0 except on IE
     content: "";
   }
 
@@ -216,6 +217,7 @@
 
     &::before {
       height: subtract(100vh, $modal-dialog-margin-y-sm-up * 2);
+      height: min-content;
     }
   }