Update OSS C* and DSE versions to the latest in gradle.properties

Update OSS C* and DSE versions to the latest in [`gradle.properties`](https://github.com/datastax/cdc-apache-cassandra/blob/master/gradle.properties#L13-L15)

- OSS C* 3.x version to `3.11.14`
- DSE version to `6.8.34`
- OSS C* 4.x version to `4.0.8`