Issue #2684141 by benjy, dawehner: Convert migrate kernel tests to KernelTestBaseTNG

.../tests/src/Kernel/Migrate/d6/MigrateActionConfigsTest.php

...action/tests/src/Kernel/Migrate/d6/MigrateActionsTest.php

...action/tests/src/Kernel/Migrate/d7/MigrateActionsTest.php

...or/tests/src/Kernel/Migrate/MigrateAggregatorStubTest.php

...ts/src/Kernel/Migrate/d6/MigrateAggregatorConfigsTest.php

...tests/src/Kernel/Migrate/d6/MigrateAggregatorFeedTest.php

...tests/src/Kernel/Migrate/d6/MigrateAggregatorItemTest.php

...tests/src/Kernel/Migrate/d7/MigrateAggregatorFeedTest.php

...tests/src/Kernel/Migrate/d7/MigrateAggregatorItemTest.php

...s/src/Kernel/Migrate/d7/MigrateAggregatorSettingsTest.php

...ban/tests/src/Kernel/Migrate/d7/MigrateBlockedIPsTest.php

...es/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php

...es/block/tests/src/Kernel/Migrate/d7/MigrateBlockTest.php

...s/src/Kernel/Migrate/MigrateBlockContentBodyFieldTest.php

.../tests/src/Kernel/Migrate/MigrateBlockContentStubTest.php

.../tests/src/Kernel/Migrate/MigrateBlockContentTypeTest.php

...t/tests/src/Kernel/Migrate/d6/MigrateBlockContentTest.php

...nt/tests/src/Kernel/Migrate/d7/MigrateCustomBlockTest.php

...ok/tests/src/Kernel/Migrate/d6/MigrateBookConfigsTest.php

...ules/book/tests/src/Kernel/Migrate/d6/MigrateBookTest.php