raise dependency on PHP 8.0

keep compatibility using laminas-zendframework-bridge
  as this is only used using compat autolader
raise dependency on zend-loader >= 2.8
raise dependency on zend-stdlib >= 3.6
raise dependency on zend-uri >= 2.9.1
raise dependency on zend-validator >= 2.15

raise dependency on PHP 7.3
switch to phpunit9