CI: Use the correct key when looking up OpenSSL

While working on the CI, I ended up changing the scheme used for the key,
but as the old scheme had been looked up successfully in my fork,
it didn't break until it landed on master.

Author: Geod24

.github/workflows/ci.yml

@@ -87,7 +87,7 @@ jobs:
       uses: actions/cache@v1
       with:
         path: ${{ github.workspace }}/openssl/
-        key: ${{ matrix.os }}-${{ matrix.openssl.version }}
+        key: ${{ runner.os }}-${{ runner.arch }}-${{ matrix.openssl.version }}
 
     - name: 'Make sure OpenSSL was loaded from cache'
       if: steps.lookup-openssl.outputs.cache-hit != 'true'