refactor: enable strict checks (#16168)

.eslintrc.js

.github/workflows/build.yml

lib/config/migration.ts

lib/config/options/index.spec.ts

lib/config/presets/gitea/index.ts

lib/config/presets/index.spec.ts

lib/config/presets/local/common.ts

lib/config/presets/local/index.ts

lib/config/presets/npm/index.ts

lib/config/validation.ts

lib/modules/datasource/crate/index.ts

lib/modules/datasource/docker/index.ts

lib/modules/datasource/galaxy/index.ts

lib/modules/datasource/github-tags/index.ts

lib/modules/datasource/gitlab-tags/index.ts

lib/modules/datasource/index.spec.ts

lib/modules/datasource/index.ts

lib/modules/datasource/npm/npmrc.ts

lib/modules/datasource/packagist/index.ts

lib/modules/datasource/rubygems/get-rubygems-org.ts