refactor(lib/workers): fix null-check for tests (#16163)

lib/config/migration.ts

lib/workers/global/index.spec.ts

lib/workers/repository/config-migration/branch/index.spec.ts

lib/workers/repository/config-migration/branch/index.ts

.../repository/config-migration/branch/migrated-data.spec.ts

lib/workers/repository/config-migration/pr/index.spec.ts

lib/workers/repository/dependency-dashboard.spec.ts

lib/workers/repository/errors-warnings.spec.ts

lib/workers/repository/extract/file-match.spec.ts

lib/workers/repository/extract/manager-files.ts

lib/workers/repository/finalise/prune.ts

lib/workers/repository/init/merge.spec.ts

lib/workers/repository/init/semantic.spec.ts

lib/workers/repository/init/vulnerability.spec.ts

lib/workers/repository/model/semantic-commit-message.spec.ts

lib/workers/repository/onboarding/branch/index.spec.ts

lib/workers/repository/onboarding/pr/index.spec.ts

lib/workers/repository/process/fetch.spec.ts

lib/workers/repository/process/fetch.ts

lib/workers/repository/process/limits.spec.ts