Update docker workflow

[gpmayorga]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Changes and Descriptions

[List your changes here]

Checklist:

• I have added Rust doc comments to structs, enums, traits and functions
• I have made corresponding changes to the documentation
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works

[wischli]

LGTM

[gpmayorga]

I'd consider this ready to merge pending the decision if we want to go for the 4-core option (1h 15min build time) or the 8-core option (45 min build time)

[wischli]

Since the 4-core docker build (72 min = 1.152$) is a bit more cost-efficient than the 8-core (42 min = 1.344$), this seems to be the way.

Source: https://docs.github.com/en/billing/managing-billing-for-github-actions/about-billing-for-github-actions#per-minute-rates