Switch to using a secret for the hook url in the CI job

Author: andybalaam

.github/workflows/latest-matrix-sdk-crypto.yml

@@ -81,7 +81,7 @@ jobs:
         if: failure()
         uses: fjogeleit/http-request-action@v1
         with:
-          url: 'https://element.ems.host/hookshot/webhook/4bbf3b21-e94a-4a97-8a09-c0e03a6de173'
+          url: ${{ secrets.CRYPTO_HOOK_URL }}
           method: 'POST'
           customHeaders: '{"Content-Type": "application/json"}'
           data: '{"text": "matrix-rust-sdk-crypto-wasm is failing to build against the latest matrix-sdk Rust code. See ${{ steps.create-issue.outputs.url }}"}'