7 files declare their use of ParserInterface in Feeds 8.3

FeedTest.php in tests/src/Kernel/Entity/FeedTest.php

FeedTypeTest.php in tests/src/Unit/Entity/FeedTypeTest.php

OpmlParser.php in src/Feeds/Parser/OpmlParser.php

ParserBase.php in src/Feeds/Parser/ParserBase.php

ParserWithMappingForm.php in tests/modules/feeds_test_plugin/src/Feeds/Parser/ParserWithMappingForm.php

SitemapParser.php in src/Feeds/Parser/SitemapParser.php

SyndicationParser.php in src/Feeds/Parser/SyndicationParser.php