fix: align z-index with "sticky" level

Author: iobuhov

packages/modules/data-widgets/src/themesource/datawidgets/web/_datagrid-filters.scss

@@ -70,7 +70,7 @@ $dg-item-min-height: 32px;
     padding: 0;
     margin: 0;
     background: var(--bg-color-secondary, $dg-background-color);
-    z-index: 55;
+    z-index: 51;
     border-radius: 8px;
     list-style-type: none;
     box-shadow: 0 2px 20px 1px rgba(5, 15, 129, 0.05), 0 2px 16px 0 rgba(33, 43, 54, 0.08);

packages/modules/data-widgets/src/themesource/datawidgets/web/_datagrid-scroll.scss

@@ -1,7 +1,7 @@
 .container-stuck + .table .th {
     position: -webkit-sticky; /* Safari */
     position: sticky;
-    z-index: 10;
+    z-index: 50;
 }
 
 /**
@@ -10,7 +10,7 @@
  * If we moved headers out of the grid body, please, remove this piece of guano.
  */
 .container-stuck + .table .th:has(.filter-selectors.visible) {
-    z-index: 20;
+    z-index: 51;
 }
 
 .widget-datagrid-content.infinite-loading {