chore(ci): linting job changes regarding goheader

[qdm12]

Why this should be merged

goheader only needs to be run on files changed in the current PR as it will otherwise suggest updating copyright years on untouched files. The other linters, however, should be run in the same manner as a local invocation.

(this was thought about in #115)

How this works

• golangci-lint runs in its own job step as configured in .golangci.yml (same as locally)
• goheader runs in its own job step on new issues only

How this was tested

Linting CI passing

[ARR4N]

Why is this necessary? What is it about --enable that's insufficient?

[qdm12]

So this only enables goheader in that CI step, so that it runs on new changes.
The rest (as locally) runs in another CI step, on everything (matching the "libevm" file path), not just new changes

--enable enables on top of existing linters, whereas --enable-only enables just that goheader linter and disables all other linters

[ARR4N]

Thanks for the clarification. I've modified the PR description because I don't think it captured the rationale.