[flink-playgrounds] Use more recent MySQL image built for linux/arm64/v8 & linux/amd64

Trying to work through the https://nightlies.apache.org/flink/flink-docs-master/docs/try-flink/table_api/, I ran into issues w/ my M1 macbook pro. It looks like mysql:8.0.19 hasn't been built for linux/arm64/v8. With a more recent version of mysql, the example starts correctly. Tried to look to see if there were any other tickets, but I couldn't seem to find any. I'll attach a PR, but this is low priority as I was able to just update the docker-compose.yaml.