core: fix TestMemCachedPersist test

Problem:
```
--- FAIL: TestMemCachedPersist (0.07s)
    --- FAIL: TestMemCachedPersist/BoltDBStore (0.07s)
        testing.go:894: TempDir RemoveAll cleanup: remove C:\Users\Anna\AppData\Local\Temp\TestMemCachedPersist_BoltDBStore294966711\001\test_bolt_db: The process cannot access the file because it is being used by another process.
```

Solution:
Release the resources occupied by the DB.

pkg/core/storage/memcached_store_test.go

@@ -109,6 +109,10 @@ func TestMemCachedPersist(t *testing.T) {
 	})
 	t.Run("BoltDBStore", func(t *testing.T) {
 		ps := newBoltStoreForTesting(t)
+		t.Cleanup(func() {
+			err := ps.Close()
+			require.NoError(t, err)
+		})
 		testMemCachedStorePersist(t, ps)
 	})
 }