Applying black formatting

- Fixing flake8 configuration to agree with black
- Adding black validation check to github actions

scripts/capnp_test_pycapnp.py

@@ -3,7 +3,10 @@ import os
 import sys
 
 import capnp
-capnp.add_import_hook([os.getcwd(), "/usr/local/include/"])  # change this to be auto-detected?
+
+capnp.add_import_hook(
+    [os.getcwd(), "/usr/local/include/"]
+)  # change this to be auto-detected?
 
 import test_capnp  # noqa: E402
 
@@ -20,7 +23,7 @@ def encode(name):
     print(message.to_bytes())
 
 
-if sys.argv[1] == 'decode':
+if sys.argv[1] == "decode":
     decode(sys.argv[2])
 else:
     encode(sys.argv[2])