* Install requited locale in container image
One of the IMAP tests curiuosly ran successfully on Github-runners, but
failed locally. This is the pre-condition for a fix.
* Explicitly require mandatory locale for test
This test works only if executed with LC_COLLATE=en_US
* Schedule to rebuild testrunner image each week
* Check plugins composer.json using CI
* Add "require-dev" and "config.allow-plugins" to plugins
* fix composer.json format - rm invalid email
* fix composer.json format - fix ext require
* fix composer.json format - fix plugin name
* tmp
* Revert "tmp"
* fix ext in ext install
* disable plugin in plugin install until Roundcube is fully autoloadable
* fix composer.json format - fix non-canonical license name
* Revert "Add "require-dev" and "config.allow-plugins" to plugins"
* no composer install for plugins needed
* Revert "fix ext in ext install"
* add standard "Test" suffix to phpunit files
* rm unneeded "suffix" in phpunit config
* simplify phpunit config
* fix default "xhtml" doctype in unit testing
* fix test_format_date test to not rely on other tests
* even more phpunit config simplify
* stricter/unify phpunit params for E2E tests
* run E2E tests on maximal php version too with lowest deps
* "repositories" in bundled plugins are useless as for root package only
* add/unify missing plugin test
