src: Fix "Table headers must have an accessible name" warning

The tests output contained following warning:

```
console.warn
    Th: Table headers must have an accessible name. If the Th is intended to be visually empty, pass in screenReaderText. If the Th contains only non-text, interactive content such as a checkbox or expand toggle, pass in an aria-label.
```

This fixes the warning by adding an `aria-label` to every empty table heading cell.

src/Components/CreateImageWizardV2/steps/Repositories/Repositories.tsx

@@ -535,7 +535,7 @@ const Repositories = () => {
                 <Table variant="compact" data-testid="repositories-table">
                   <Thead>
                     <Tr>
-                      <Th />
+                      <Th aria-label="Selected" />
                       <Th width={45}>Name</Th>
                       <Th width={15}>Architecture</Th>
                       <Th>Version</Th>