docker-compose.yml: add --colors=auto to phpunit
docker-compose.yml: add --colors=auto to phpunit

This forces colors to display in the terminal when phpunit is run with
composer (since it makes phpunit think the output is not a TTY).

This may need to be reverted if it causes the GitHub Action captured
output to be filled with escape characters.

smrealms/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr