ci: stop publishing the pnpm store from GitHub-hosted runners (#34588)

Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

.github/actions/install-node-dependencies/action.yml

@@ -185,9 +185,10 @@ runs:
         key: node-cache-${{ runner.os }}-${{ steps.pnpm-store.outputs.arch }}-pnpm-${{ hashFiles(inputs.cache-dependency-path) }}
 
     # Producers can refresh access and publish misses without downloading existing archives.
+    # Not on GitHub-hosted runners: nothing restores that store, and direct installs beat restoring it.
     - name: Keep pnpm download store without restoring
       id: pnpm-store-lookup
-      if: steps.pnpm-store-mode.outputs.lookup-only == 'true'
+      if: steps.pnpm-store-mode.outputs.lookup-only == 'true' && runner.environment != 'github-hosted'
       uses: actions/cache@v5
       with:
         # Twice-nested composite cleanup loses internal step outputs.

config/scripts/ci-dependency-download-cache.test.mjs

@@ -81,7 +81,9 @@ describe('CI dependency download caches', () => {
     const restore = action.runs.steps.find((step) => step.id === 'pnpm-store-restore')
     expect(action.inputs['cache-pnpm-store-lookup-only'].default).toBe('auto')
     expect(lookup.uses).toBe('actions/cache@v5')
-    expect(lookup.if).toBe("steps.pnpm-store-mode.outputs.lookup-only == 'true'")
+    expect(lookup.if).toBe(
+      "steps.pnpm-store-mode.outputs.lookup-only == 'true' && runner.environment != 'github-hosted'"
+    )
     expect(lookup.with).toEqual({
       path: '${{ env.ORCA_PNPM_STORE_CACHE_PATH }}',
       key: restore.with.key,

config/scripts/ci-pnpm-store-mode.test.mjs

@@ -76,9 +76,10 @@ describe('automatic pnpm store mode', () => {
         )
       const nodeSetup = action.runs.steps.find((step) => step.id === 'default-node')
       expect(evaluate(nodeSetup.with.cache.slice(3, -2))).toBe(cache)
-      expect(evaluate(action.runs.steps.find((step) => step.id === 'pnpm-store-lookup').if)).toBe(
-        lookup
-      )
+      const publish = action.runs.steps.find((step) => step.id === 'pnpm-store-lookup').if
+      expect(evaluate(publish)).toBe(false)
+      context.runner.environment = 'self-hosted'
+      expect(evaluate(publish)).toBe(lookup)
     }
   )