Where I work, we've moved CI "left", all tests are run on the developers machine before merging
You're not shifting left unless you guarantee local tests always run, faithfully to production. That rarely happens. Local testing should be supplementary. We use https://hk.jdx.dev/
We do ensure this, requiring signed proof, running in containers that would be identical to github runners (more or less). Now, this could be spoofed by an engineer, but we operate in a high trust environment
This is interesting. Are you using an available product for managing these signatures, or did you write your own?