Drop Support for Php 8.1

[oleibman]

This PR will be merged at the end of this month. As the README says, we maintain support for Php Versions for six months beyond their end of life. That time has now arrived for 8.1.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests
• removal of software which is no longer supported

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary