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?

[shaypal5]

We're using the following code to start MongoDB in Docker:

- name: Start MongoDB in docker
        if: matrix.backend == 'mongodb'
        run: |
          # start MongoDB in a container
          docker run -d -p ${{ env.CACHIER_TEST_PORT }}:27017 --name mongodb mongo:latest
          # wait for MongoDB to start, which is in average 5 seconds
          sleep 5
          # show running containers
          docker ps -a

Doesn't this mean we're already using the latest Docker image for MongoDB?