phpunit: --filter tests with @dataprovider

Only run one specific data provider parameter set:

$ phpunit --filter testCalculateDates4Weeks@2025W01-2

You have to use keys in the dataprovider array.

Links:

• https://phpunit.readthedocs.io/en/9.5/writing-tests-for-phpunit.html#data-providers
• https://www.vivait.co.uk/labs/running-phpunit-with-a-specific-data-provider-set