Ensure all files are unique for check-wheel-contents

[rmartin16]

Changes

• hynek/build-and-inspect-python-package runs check-wheel-contents and it requires the wheel contains zero duplicated files
• RE: Implement hynek/build-and-inspect-python-package in python-package-create.yml .github#137

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

I'm intrigued to know what this check is actually be protecting against... but no objection to complying.

[rmartin16]

fwiw, their documentation says (1) "you copied a file when you meant to rename it" or (2) "you built a wheel, renamed a file, and re-created the wheel without deleting the build directory first".

Number (2) sounds like a historical problem....but number (1) seems reasonable I guess. I'd argue, though, it is late in the process to be catching this when you're building a wheel but...