Fix pnpm dependency workflow cache and lockfile updates

`pnpm audit --fix` only writes overrides to package.json /
pnpm-workspace.yaml without refreshing pnpm-lock.yaml, so the PR
produced for security fixes had a stale lockfile. The post step
for actions/setup-node also failed with "Path Validation Error"
because the pnpm store was never populated.

Add a `pnpm install --no-frozen-lockfile` step after the audit /
update operation so the lockfile is refreshed and the pnpm store
exists for the cache post-step.

Author: Christdej

.github/workflows/pnpm_dependency_update_and_create_pr.yml

@@ -62,6 +62,16 @@ jobs:
         if: ${{ inputs.operation == 'audit-fix' }}
         run: pnpm audit --fix
 
+      # `pnpm audit --fix` only writes overrides to package.json /
+      # pnpm-workspace.yaml; it does not refresh pnpm-lock.yaml. Running
+      # `pnpm install` here both applies the overrides to the lockfile and
+      # populates the pnpm store so the `cache: pnpm` post-step in
+      # actions/setup-node has a path to cache (otherwise it fails with
+      # "Path Validation Error: Path(s) specified in the action for caching
+      # do(es) not exist").
+      - name: Install dependencies to update lockfile and populate cache
+        run: pnpm install --no-frozen-lockfile
+
       - name: Create Pull Request
         uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 #v8
         with: