fix: mark type of flat config export to satisfy Linter.Config[] (#10128)

### Description

Adds `satisfies Linter.Config[]` after the flat config definition. This
allows importing the config into other typescirpt configs without having
type unification issues.

### Testing Instructions

N/A this is a pretty simple type fix

Co-authored-by: Anthony Shew <[email protected]>

Author: cprussin

packages/eslint-config-turbo/src/flat/index.ts

@@ -1,3 +1,4 @@
+import type { Linter } from "eslint";
 import plugin from "eslint-plugin-turbo";
 
 // eslint-disable-next-line import/no-default-export -- Matching old module.exports
@@ -10,4 +11,4 @@ export default [
       "turbo/no-undeclared-env-vars": "error",
     },
   },
-];
+] satisfies Linter.Config[];