reduce powershell pr check perms

Author: dilanbhalla

.github/workflows/powershell-pr-check.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'microsoft/codeql'
     permissions:
-      contents: write
+      contents: read
     steps:
       - name: Checkout
         uses: actions/checkout@v3