Bump pin to unify lint job versions across elements (Qiskit#498)

* Bump pin to unify lint job versions across elements

In an effort to unify the versions of pylint run across all the elements
this commit bumps the pinned versions of pylint and astroid to be the
latest and what we are syncing all the elements to use. This should make
working between all the elements easier to do.

Related To: Qiskit/qiskit#3629

* Fix issues introduced by new versions

In a typical example of why we hard pin to a single version for
everything related to pylint in CI the change from 2.4.3 to 2.4.4
introduced a new rule (or changed rule behavior) that caused failures.
This commit fixes those so the new version passes.

constraints.txt

@@ -1,2 +1,2 @@
-pylint==2.4.1
-astroid==2.3.0
+pylint==2.4.4
+astroid==2.3.3

qiskit/providers/aer/noise/utils/noise_transformation.py

@@ -92,7 +92,7 @@ def approximate_quantum_error(error, *,
                 no_info_error + " for {} qubits".format(error.number_of_qubits))
         operator_dict = operator_lists[error.number_of_qubits - 1]
     if operator_dict is not None:
-        names, operator_list = zip(*operator_dict.items())
+        _, operator_list = zip(*operator_dict.items())
     if operator_list is not None:
         op_matrix_list = [
             transformer.operator_matrix(operator) for operator in operator_list