Fix Play Store publishing

Apparently pyOpenSSL no longer supports PKCS #12. We are using oauth2client,
which is obsolete and hasn't been updated in a while, that uses pyOpenSSL
under the hood.

After briefly looking around at our options, it seems that--if we want to do
things right--we could:
  * Use google-auth & friends. This doesn't support p12 though, so:
    * Somehow download a new key, or
    * Somehow convert the old key to the new format;
  * Use Gradle Play Publisher, it might support p12?

While we explore these options, let's just temporarily pin pyOpenSSL to a
version that supports PKCS #12.

googleapis/google-auth-library-python#288 (comment)
https://github.com/Triple-T/gradle-play-publisher

.github/workflows/main.yml

@@ -94,7 +94,7 @@ jobs:
       - name: Prepare environment
         run: |
           pip install --upgrade pip
-          pip install --user --upgrade google-api-python-client oauth2client httplib2 pyOpenSSL
+          pip install --user --upgrade google-api-python-client oauth2client httplib2 pyOpenSSL==22.1.0
 
       - name: Checkout repository
         uses: actions/checkout@v2