Retain two spaces between content and comment in yaml files

[rarkins]

Discussed in #31359

^{Originally posted by zisuu September 12, 2024}

Context and Proposal

By default, Renovate does not keep the two spaces between content and a comment in a yaml file when it needs to update the comment. This can lead to issues like Renovate PRs not getting merged if you have yamllint checks running, see this example Repo Pull Request: https://github.com/zisuu/yamllint-test/pull/1/files:

From:

      - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29  # v4.1.6

To:

      - uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938 # v4.2.0

Ideas on how to solve this:

• Renovate should retain the existing spacing if replacing an existing comment value (1 or 2). One space is not invalid YAML even if the main linter recommends against it
• If Renovate is adding the comment, then let's default to two spaces like the linter recommends

This applies to the lib/modules/manager/github-actions code specifically.

Reproduction forked to https://github.com/renovate-reproductions/31359