6 files declare their use of FrontendEnvironmentBase in Build Hooks 3.x

BitbucketFrontendEnvironment.php in modules/build_hooks_bitbucket/src/Plugin/FrontendEnvironment/BitbucketFrontendEnvironment.php

CircleCiFrontendEnvironment.php in modules/build_hooks_circleci/src/Plugin/FrontendEnvironment/CircleCiFrontendEnvironment.php

CircleV2.php in modules/build_hooks_circleci/src/Plugin/FrontendEnvironment/CircleV2.php

GenericFrontendEnvironment.php in src/Plugin/FrontendEnvironment/GenericFrontendEnvironment.php

NetlifyFrontendEnvironment.php in modules/build_hooks_netlify/src/Plugin/FrontendEnvironment/NetlifyFrontendEnvironment.php

TestEnvironment.php in tests/modules/build_hooks_test/src/Plugin/FrontendEnvironment/TestEnvironment.php