fix: [Dashboard > Entity Analytics: Risk Scores Table][KEYBOARD]: Ele…

…ments with keyboard focus must be visible (elastic#178317)

Closes: elastic/security-team#8624

## Description

The Overview dashboard has two buttons that are invisible on keyboard
focus. These buttons toggle modal dialogs and are only visible on hover.
Screenshot attached.

### Steps to recreate

1. Open [Entity Analytics
dashboard](https://kibana.siem.estc.dev/app/security/entity_analytics)
2. Open dev tools and type `document.activeElement` into the live
expression window to have the active element follow your focus
3. Tab through the view until focus gets "lost" or disappears in the
User Risk Scores table rows
4. Verify focus is on a button that is not visible on the page

### Screen 


https://github.com/elastic/kibana/assets/20072247/0ca8db38-006a-49ea-9019-e23078844c10

x-pack/plugins/security_solution/public/entity_analytics/components/styled_basic_table.tsx

@@ -15,17 +15,18 @@ export const StyledBasicTable = styled(EuiBasicTable)`
     }
   }
 
-  .inlineActions {
+  .inlineActions button {
     opacity: 0;
   }
 
   .EntityAnalyticsTableHoverActions {
-    .inlineActions-popoverOpen {
+    .inlineActions-popoverOpen button {
       opacity: 1;
     }
 
-    .inline-actions-table-cell:hover {
-      .inlineActions {
+    .inline-actions-table-cell {
+      .inlineActions button:focus-visible,
+      &:hover .inlineActions button {
         opacity: 1;
       }
     }