Replace deprecated assertRegExp() with assertMatchesRegularExpression()

[andypost]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	yes
Related tickets	follow-up to #45
Documentation	TBD
License	MIT

What's in this PR?

In #45 compatibility with phpunit 9.3 was declared
But 9.3 throws warnings now on usage of assertRegExp() replaced with assertMatchesRegularExpression() in phpinit 9.1
Ref https://phpunit.readthedocs.io/en/9.1/assertions.html#assertmatchesregularexpression

Why?

Testing laminas/laminas-diactoros#46 travis reports this warnings because it using php 8 (nightly) so composer resolves phpunit to 9.3
Also package tests reports the same https://travis-ci.org/github/php-http/psr7-integration-tests/jobs/738863983#L393

Checklist

• Updated CHANGELOG.md to describe BC breaks / deprecations | new feature | bugfix
• Documentation pull request created (if not simply a bugfix)

To Do

• If the PR is not complete but you want to discuss the approach, list what remains to be done here

[dbu]

thanks for looking into this. unfortunately, phpunit 9 does not run on PHP 7.2, so the builds for 7.2 now fail because the new method is not available. i think the solution is to add a method to the MessageTrait that does a method_exists check and falls back to the old assertion if it does not exist.

[andypost]

Good idea, thank you! Will update soon.

[andypost]

Fixed both places and added to todo to remove later

[andypost]

@dbu thank you a lot! looks I need another coffee 🤦

[dbu]

thanks, now it looks fine 👍