Fix import of mirror qv circuit function (#2570)

mitiq/benchmarks/__init__.py

@@ -8,6 +8,7 @@
     generate_rotated_rb_circuits,
 )
 from mitiq.benchmarks.mirror_circuits import generate_mirror_circuit
+from mitiq.benchmarks.mirror_qv_circuits import generate_mirror_qv_circuit
 from mitiq.benchmarks.ghz_circuits import generate_ghz_circuit
 from mitiq.benchmarks.quantum_volume_circuits import (
     generate_quantum_volume_circuit,