fix: Update stable Helm repo URL (#8251)

docs/usage/configuration-options.md

lib/datasource/helm/__fixtures__/index.yaml

lib/datasource/helm/index.ts

lib/manager/ansible-galaxy/__fixtures__/helmRequirements.yml

lib/manager/helm-requirements/index.ts

lib/manager/helmfile/__snapshots__/extract.spec.ts.snap

lib/manager/helmfile/extract.spec.ts

lib/manager/helmfile/index.ts

lib/manager/helmv3/__snapshots__/extract.spec.ts.snap

lib/manager/helmv3/extract.spec.ts

lib/manager/helmv3/index.ts

lib/manager/regex/__snapshots__/index.spec.ts.snap

lib/manager/regex/index.spec.ts

lib/manager/terraform/__fixtures__/helm.tf

lib/manager/terraform/__snapshots__/extract.spec.ts.snap