Update container name separator to hyphen to match Docker Compose v2

[uosis]

Quoting Docker docs:

In Compose v1, an underscore (_) was used as the word separator. In Compose v2, a hyphen (-) is used as the word separator.

Mismatch causes issues like this.

[p12tic]

Someone needs to revive #1080

[p12tic]

I think the issue can stay opened until that PR is merged.