Updating digest for v2 Golang package loses the version

[Cerber-Ursi]

How are you running Renovate?

Self-hosted Renovate

If you're self-hosting Renovate, tell us which platform (GitHub, GitLab, etc) and which version of Renovate.

GitLab, Renovate v40.5.1 via Docker image

Please tell us more about your question or problem

Context

For one of our Golang dependencies, we use the digest-pinned version from v2 branch, since, on the one hand, we need some functionality that exists only in v2, on the other hand, there is a regression in v2, fix for this regression is in the repository, but not released yet. This digest is not the newest commit from the corresponding branch, therefore Renovate sees it as a possibly-needs-updating dependency and issues a merge request.

Expected behavior

Renovate either updates version correctly, or skips update fully.

Actual behavior

Renovate tries to update dependency to the latest digest on the master branch, instead of v2 branch, and the build fails with go.mod has non-.../v2 module path.

Reproduction

I managed to reproduce this on Github with Mend.io-hosted app - https://github.com/Cerber-Ursi/renovate-golang-v2-digest.

Extra

Possibly connected problem - issue #20316.

Logs (if relevant)

No response