👷‍♀️ Build against MongoDB v5.0

MongoDB 4.4 will be [end-of-lifed in February][1]. This change runs the
build against MongoDB 5.0 in readiness for upgrading our Staging and
Production replica sets.

[1]: https://www.mongodb.com/support-policy/lifecycles

Author: alecgibson

.github/workflows/test.yml

@@ -16,6 +16,7 @@ jobs:
       matrix:
         mongodb:
         - 4.4
+        - 5.0
         mongo_driver:
         - mongodb4
         - mongodb5