ci: golangci-lint used via make tools instead of golangci-lint-action

Problem

Skopeo CI installs golangci-lint at runtime via make tools in the validate and osx jobs, then runs make validate-local.

Podman uses golangci/golangci-lint-action (install-only) with the version read from the Makefile.

The skopeo_cidev CI image includes golang but not golangci-lint.

Review context

Sandbox GHA migration review (mtrmac, PR #1) noted this as a future improvement, marked "not now":

• validate job: eventually use the golangci-lint GitHub action
• osx job: eventually better with golangci-lint's GitHub action

Related review also asked about actions/setup-go caching vs using Fedora RPM Go in container jobs.

Related

• Podman reference: validate-source job in .github/workflows/ci.yml
• Podman disabled golangci-lint-action caching due to flaky results (podman#28893)