Disable fuzzing on upgradeable contracts

(cherry picked from commit 9416743a1079f35320173b8809e9a28ae8444128)

.github/workflows/checks.yml

@@ -44,6 +44,7 @@ jobs:
           token: ${{ github.token }}
 
   foundry-tests:
+    if: github.repository != 'OpenZeppelin/openzeppelin-contracts-upgradeable'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3