Make mypy pass no matter if qsimcirq is installed or not (#7063)

Avoid `[unused-ignore]` error when qsimcirq is installed.

Author: pavoljuhas

cirq-google/cirq_google/engine/virtual_engine_factory.py

@@ -402,7 +402,7 @@ def create_default_noisy_quantum_virtual_machine(
 
     if simulator_class is None:
         try:  # pragma: no cover
-            import qsimcirq  # type: ignore
+            import qsimcirq
 
             simulator_class = qsimcirq.QSimSimulator  # pragma: no cover
         except ImportError:

dev_tools/conf/mypy.ini

@@ -16,7 +16,7 @@ ignore_missing_imports = true
 # 3rd-party libs for which we don't have stubs
 
 # Google
-[mypy-google.api_core.*,google.auth.*,google.colab.*,google.cloud.*,google.oauth2.*]
+[mypy-google.api_core.*,google.auth.*,google.colab.*,google.cloud.*,google.oauth2.*,qsimcirq]
 follow_imports = silent
 ignore_missing_imports = true