Freeze mypy to 0.942

We're facing an issue where mypy is compalining that we're missing
an await on `asyncio.sleep(polling_interval)` in
astronomer/providers/apache/hive/hooks/hive.py:46
This is potentially because of the new release of mypy==0.950
including PR python/mypy#12279
We don't face this issue with mypy==0.942 and hence, freezing it.

setup.cfg

@@ -87,7 +87,7 @@ tests =
     pytest-cov
     pre-commit
 mypy =
-    mypy>=0.800
+    mypy==0.942
     types-aiofiles
     types-boto
     types-certifi