Pin pnpm to v10 in CI workflows to fix ERR_PNPM_UNSUPPORTED_ENGINE

[yomybaby]

Problem

GitHub Actions workflows install pnpm via pnpm/action-setup@v{4,5} with version: latest, which now resolves to pnpm 11.0.8. This conflicts with this repo's engines.pnpm: ^10.16.0 constraint and engine-strict=true in .npmrc, breaking every CI run with:

ERR_PNPM_UNSUPPORTED_ENGINE
Expected version: ^10.16.0
Got: 11.0.8

Example failure: https://github.com/lablup/backend.ai-webui/actions/runs/25532505739/job/74941615237 (PR #7289 react-vitest)

Why pnpm v10 (not v11)

pnpm v11 is a major release with multiple breaking changes (Node 22+, pnpm field in package.json removed, onlyBuiltDependencies replaced with allowBuilds, .npmrc scope reduced, etc.) — this repo currently has pnpm.overrides in package.json and onlyBuiltDependencies in pnpm-workspace.yaml that would break under v11. A proper v11 migration belongs in a separate, scoped task.

Scope

Pin pnpm/action-setup to version: 10 (latest 10.x) in:

• .github/workflows/vitest.yml (3 occurrences)
• .github/workflows/package.yml (4 occurrences)
• .github/workflows/publish-backend.ai-ui.yml (1)
• .github/workflows/publish-backend.ai-docs-toolkit.yml (1)
• .github/workflows/weekly-merge-branch-lockfiles.yml (1)

Out of scope

• Upgrading to pnpm v11 (tracked separately).
• Touching engines.pnpm, pnpm-workspace.yaml, pnpm-lock.yaml, or any application code.

Acceptance

• All affected workflows use version: 10.
• A test PR's CI passes the install step.

JIRA Issue: FR-2839