CI: fix docker pushes

[casperdcl]

Fixes #41

ref	image
PR	- (just test)
master	wemakeservices/caddy-gen:master, ghcr.io/wemake-services/caddy-gen:master
tag M.m.p	wemakeservices/caddy-gen:M.m.p, wemakeservices/caddy-gen:latest, ghcr.io/wemake-services/caddy-gen:M.m.p, ghcr.io/wemake-services/caddy-gen:latest

[casperdcl]

@sobolevn this is ready for merge now. It'll push to ghcr.io/wemake-services/caddy-gen.

If you want to push to wemakeservices/caddy-gen too, then you'll have to add DOCKER_USER and DOCKER_PASS env vars to https://github.com/wemake-services/caddy-gen/settings/secrets/actions

[casperdcl]

done ;)

[casperdcl]

ping :)

[sobolevn]

Thank you!