test: check scanning field from getwalletinfo

During a rescan, check that `getwalletinfo` returns
properly information (the scanning field) about it.

test/functional/wallet_importdescriptors.py

@@ -705,6 +705,7 @@ def run_test(self):
             except JSONRPCException as e:
                 assert e.error["code"] == -4 and "Error: the wallet is currently being used to rescan the blockchain for related transactions. Please call `abortrescan` before changing the passphrase." in e.error["message"]
 
+            assert_equal(self.nodes[0].cli("-rpcwallet=encrypted_wallet").getwalletinfo()["scanning"], {'duration': 1, 'progress': 0})
             assert_equal(importing.result(), [{"success": True}])
 
         assert_equal(temp_wallet.getbalance(), encrypted_wallet.getbalance())