actions: decrease image-version to 18.04

[rommelfreddy]

No description provided.

[rommelfreddy]

this should be only a temporary change.
Maybe we should add phpstan and different php-versions to the image.

• php 5.6
• php 7.x
• php 8.x

[eiriarte-mendez]

Hi @rommelfreddy ,
hmm checks are still failing ...

Your requirements could not be resolved to an installable set of packages.

 Problem 1
   - phpunit/phpunit[5.7.0, ..., 5.7.27] require php ^5.6 || ^7.0 -> your php version (8.0.2) does not satisfy that requirement.
   - Root composer.json requires phpunit/phpunit 5.7.* -> satisfiable by phpunit/phpunit[5.7.0, ..., 5.7.27].

I think I will refactor the tests a bit and upgrade phpunit... but thx for trying ...

[eiriarte-mendez]

this should be only a temporary change.
Maybe we should add phpstan and different php-versions to the image.

php 5.6
php 7.x
php 8.x

I will also try that