fix(pnpm-install): pin lock-hash to a step output so cache-save survives teardown

`actions/cache@v4` re-evaluates `key:` in its post-step (cache-save) at job
teardown. On some self-hosted / k8s runners the workspace is wiped before
the post-step runs, so `hashFiles('**/pnpm-lock.yaml')` returns no files
and fails the entire job — even when every real step has already passed.

Capture the hash once in a regular `run:` step (where `hashFiles` is
evaluated against the live workspace) and feed the resulting value into
the cache `key:` via `steps.pnpm-lock-hash.outputs.HASH`. Step outputs
are stored in the runner's `_temp/` state and survive workspace teardown,
so the post-step evaluation of `key:` no longer touches the filesystem.

Functionally equivalent on healthy runners — same hash, same cache key.

Observed in the wild against `apify-core`: cypress shard 6 of run
https://github.com/apify/apify-core/actions/runs/25511344092, where all
41 specs passed but the job was failed by `Post Install dependencies`
with `hashFiles('**/pnpm-lock.yaml') failed. Fail to hash files under
directory '/home/runner/_work/apify-core/apify-core'`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: B4nan

pnpm-install/action.yaml

@@ -67,11 +67,23 @@ runs:
       run: |
         echo "YEAR_MONTH=$(/bin/date -u "+%Y%m")" >> $GITHUB_OUTPUT
 
+    # Pre-compute the lockfile hash and store it as a step output. `actions/cache@v4`
+    # re-evaluates `key:` in its post-step (cache-save) at job teardown, and on some
+    # self-hosted/k8s runners the workspace is wiped before that runs — calling
+    # `hashFiles('**/pnpm-lock.yaml')` from the post-step then fails the job after
+    # all real steps have already passed. Capturing the hash once here pins the
+    # value to a step output, which survives teardown.
+    - name: Compute pnpm-lock.yaml hash
+      id: pnpm-lock-hash
+      shell: bash
+      run: |
+        echo "HASH=${{ hashFiles('**/pnpm-lock.yaml') }}" >> $GITHUB_OUTPUT
+
     - uses: actions/cache@v4
       name: Setup pnpm cache
       with:
         path: ${{ steps.pnpm-config.outputs.STORE_PATH }}
-        key: ${{ runner.os }}-pnpm-store-cache-${{ steps.cache-rotation.outputs.YEAR_MONTH }}-${{ hashFiles('**/pnpm-lock.yaml') }}
+        key: ${{ runner.os }}-pnpm-store-cache-${{ steps.cache-rotation.outputs.YEAR_MONTH }}-${{ steps.pnpm-lock-hash.outputs.HASH }}
         restore-keys: |
           ${{ runner.os }}-pnpm-store-cache-${{ steps.cache-rotation.outputs.YEAR_MONTH }}-