ci: use distinct concurrency groups for clang and go linters

[vporoshok]

Summary

• Both clang_lint.yaml and golang_lint.yaml share name: Linter and the concurrency group ${{ github.workflow }}-${{ github.ref }}. Since github.workflow is the workflow name, both files resolved to the same group (Linter-<ref>).
• With cancel-in-progress: true, the two linters ended up in one concurrency group and cancelled each other — the clang lint job was killed with Canceling since a higher priority waiting request for Linter-... exists whenever the Go linter started on the same ref (and vice versa).
• Give each workflow its own literal group so they run independently per ref:
  • clang: clang-lint-${{ github.ref }}
  • golangci: golangci-lint-${{ github.ref }}

cancel-in-progress: true is kept, so a new push to the same PR still supersedes the previous in-progress run of that same linter.

Test plan

• Open/push a PR touching pp/** and Go files; confirm both clang-lint and golangci run to completion without cancelling each other.

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