ci: investigate how to support wildcard Go versions like 1.18.x

[leitzler]

Investigate what we need to do to be able to specify Go version as, for example, 1.18.x instead of the current way where we specify exact version, e.g. 1.18.1.

How to handle creation of docker images pushed to docker hub for example.

[mvdan]

Assuming you just need to know what Go version was selected, is it not possible to run go env GOVERSION somewhere? That will give e.g. go1.18 for tagged versions.

If you can't easily execute Go itself to obtain the version string in the YAML, then the right way would be to use an Action output from setup-go. Unfortunately it doesn't have a "selected go version" output just yet, but actions/setup-go#85 does that.