ci: prevent pnpm-cache from running on forked repo (DefinitelyTyped#72268)

Co-authored-by: Jake Bailey <[email protected]>

Author: hkleungai

.github/workflows/pnpm-cache.yml

@@ -9,6 +9,7 @@ on:
 jobs:
   create-cache:
     runs-on: ubuntu-latest
+    if: ${{ github.repository == 'DefinitelyTyped/DefinitelyTyped' }}
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - uses: actions/setup-node@cdca7365b2dadb8aad0a33bc7601856ffabcc48e # v4.3.0