feat!: remove BUILDPACK env support

lib/modules/manager/bundler/artifacts.spec.ts

lib/modules/manager/cargo/artifacts.spec.ts

...es/manager/cocoapods/__snapshots__/artifacts.spec.ts.snap

lib/modules/manager/cocoapods/artifacts.spec.ts

lib/modules/manager/composer/artifacts.spec.ts

lib/modules/manager/gomod/artifacts.spec.ts

lib/modules/manager/gradle-wrapper/artifacts.spec.ts

lib/modules/manager/gradle/artifacts.spec.ts

lib/modules/manager/helmfile/artifacts.spec.ts

...dules/manager/helmv3/__snapshots__/artifacts.spec.ts.snap

lib/modules/manager/maven-wrapper/artifacts.spec.ts

lib/modules/manager/mix/__snapshots__/artifacts.spec.ts.snap

lib/modules/manager/nix/artifacts.spec.ts

lib/modules/manager/npm/post-update/lerna.spec.ts

lib/modules/manager/npm/post-update/npm.spec.ts

lib/modules/manager/npm/post-update/pnpm.spec.ts

lib/modules/manager/npm/post-update/yarn.spec.ts

lib/modules/manager/nuget/artifacts.spec.ts

lib/modules/manager/pep621/artifacts.spec.ts

lib/modules/manager/pep621/processors/pdm.spec.ts