According to Python's formatting rules, default parameters without types
should have no spaces around the equals operator. However, if the type of
a parameter _is_ specified, spaces around the operator are required. See
also PEP-3107 for examples of such code.

Flake8 only started reporting this formatting error starting with version
3.6 (error code E252), causing our test pipeline to fail even though there
were no changes to the codebase. This commit makes sure that the
formatting checks pass again.