ci: bump pnpm/action-setup from 4 to 5

Supersedes #61, which conflicted after the actions/setup-node bump in #60
touched adjacent lines.

Author: yashranaway

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - uses: pnpm/action-setup@v5
       - uses: actions/setup-node@v7
         with:
           node-version: 24
@@ -91,7 +91,7 @@ jobs:
     timeout-minutes: 20
     steps:
       - uses: actions/checkout@v4
-      - uses: pnpm/action-setup@v4
+      - uses: pnpm/action-setup@v5
       - uses: actions/setup-node@v7
         with:
           node-version: 24