tests/cpydiff/modules_struct_whitespace_in_format: Run black.

This test snuck through without proper formatting and is causing CI for
other unrelated changes to fail.

Signed-off-by: David Lechner <david@pybricks.com>

tests/cpydiff/modules_struct_whitespace_in_format.py

@@ -7,7 +7,7 @@ workaround: Don't use spaces in format strings.
 import struct
 
 try:
-    print(struct.pack('b b', 1, 2))
+    print(struct.pack("b b", 1, 2))
-    print('Should have worked')
+    print("Should have worked")
 except:
-    print('struct.error')
+    print("struct.error")