move from defunct travis to github workflow

[dbu]

Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Related tickets	fix #50
Documentation	README.md is being updated
License	MIT

What's in this PR?

Use github workflow to run the test suite with the known implementaitons

Why?

travis-ci no longer works

To Do

• Adjust readme to link to github action runs

[dbu]

this runs the tests again and shows the problems.

• laminas is the only implementation that has green builds (but only with PHP 8, some things have not been fixed in legacy versions that still support PHP 7). i wonder if we should only build with 8, or should allow failures with php 7
• guzzle and slim have only a few failures
• nyholm should be green when 1.6 is released (it is using these integration tests in its own test suite)
• ring central looks much less close to the expectations

@GrahamCampbell are you currently maintaining guzzle? there seem to be some missing validations, do you think we can fix them in guzzle?

[GrahamCampbell]

Thanks for the ping. We're are of this issue, and will look into it soon.