fix: [Dashboard > Overview][AXE-CORE]: Select menus must have accessible labels (#177837)

Closes: https://github.com/elastic/security-team/issues/8556

## Description

The [axe browser plugin](https://deque.com/axe) is reporting two select
menus without accessible labels.

### Steps to recreate

1. Open the Security Dashboards, then click
[Overview](https://kibana.siem.estc.dev/app/security/overview)
2. Run an axe browser scan in Chrome, Edge, or Firefox
3. Verify the Critical issue "Select element must have an accessible
name"


### What was done
- Added required `a11y` attributes

### Screens

#### Axe report


![image](a79347ca-edda-42e6-873f-b87ecbab0216)

---------

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/cases/public/components/recent_cases/filters/index.tsx

@@ -67,6 +67,7 @@ export const RecentCasesFilters = React.memo<{
       onChange={onChange}
       options={options}
       value={filterBy}
+      aria-label={i18n.RECENT_CASES}
     />
   );
 });

x-pack/plugins/security_solution/public/common/components/matrix_histogram/index.tsx

@@ -341,6 +341,7 @@ export const MatrixHistogramComponent: React.FC<MatrixHistogramComponentProps> =
                     options={stackByOptions}
                     prepend={i18n.STACK_BY}
                     value={selectedStackByOption?.value}
+                    aria-label={i18n.STACK_BY}
                   />
                 )}
               </EuiFlexItem>