Bump up dev dependency qiskit-aer to 0.10.4 (#5661)
Bump up dev dependency qiskit-aer to 0.10.4 (#5661)

Both qiskit-aer and its dependency qiskit-terra attempt to write
qiskit/providers/__init__.py.  If the version from qiskit-aer 0.9.1
wins it causes broken import of qiskit.providers.aer.

This fixes failing CI checks for Python 3.8 such as
https://github.com/quantumlib/Cirq/runs/7139878042.
quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq