fix postgres in CI

Otherwise we get:

Health check error:
ContainerStart: Error response from daemon: Cannot link to a non running container: /runner-0277ea0f-project-6940217-concurrent-0-postgres-0 AS /runner-0277ea0f-project-6940217-concurrent-0-postgres-0-wait-for-service/service (docker.go:1322:0s)
Service container logs:
2020-03-22T15:26:04.873032618Z Error: Database is uninitialized and superuser password is not specified.
2020-03-22T15:26:04.873375192Z        You must specify POSTGRES_PASSWORD to a non-empty value for the
2020-03-22T15:26:04.873384826Z        superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".
2020-03-22T15:26:04.873388493Z 
2020-03-22T15:26:04.873391294Z        You may also use "POSTGRES_HOST_AUTH_METHOD=trust" to allow all
2020-03-22T15:26:04.873394348Z        connections without a password. This is *not* recommended.
2020-03-22T15:26:04.873397295Z 
2020-03-22T15:26:04.873400143Z        See PostgreSQL documentation about "trust":
2020-03-22T15:26:04.873403116Z        https://www.postgresql.org/docs/current/auth-trust.html

Also, the tests hard-code this password, so I'm not sure how this would have worked otherwise?