v1.3.0

This is a compatibility release to ensure a smooth upgrade path for those not
yet on Promise v3. We encourage upgrading to the latest version when possible,
as Promise v3 will be the way forward for this project.

• Feature: Full PHP 8.3 compatibility.
  (#257 by @clue)

• Improve test suite, use GitHub actions for continuous integration (CI) and
  report failed assertions.
  (#242 by @clue and #175, #184, #187, #216 and #218 by @SimonFrings)