Upgrade CI Mongo server version

[gencurrent]

When testing async Mongo caching on CI, I end up with this error:

E           pymongo.errors.ConfigurationError: Server at 127.0.0.1:27019 reports wire version 7, but this version of PyMongo requires at least 8 (MongoDB 4.2).

Report example:

• https://github.com/python-cachier/cachier/actions/runs/22005125468/job/63587027714?pr=334

Can we upgrade the Mongo server version in the CI environment?