The next minor version 20.2.0 has this test removed as part of removing support for Python2 and 3.5, see commit https://github.com/hynek/structlog/commit/f65309d4f66fbd44c09288a485107d725c3da1d4#diff-673441c4b6dbee451d8130f1e9bb48f3dbc44d5d3acf1c21d52d0904002342d5
So it might be justified to simply remove or disable this test until the next version-upgrade is done for the package.
