fix outmoded x and x or y idiom in infixowl.py

[ghost]

Summary of changes

Change x and x or y idiom for modern, clearer y if x is None else x, as suggested by sonarcloud analysis

Checklist

• Checked that there aren't other open pull requests for the same change.
• Checked that all tests and type checking passes.
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[coveralls]

Coverage remained the same at 88.437% when pulling a22ad4e on gjhiggins:fix-infixowl-old-idiom-use into a3a4611 on RDFLib:master.

[aucampia]

LGMT

[aucampia]

Will merge by 2022-05-25 if there is no further feedback.