infra: Automate SHA procedure during releases

[emdneto]

Description

This PR tries to automate the SHA procedure during releases. The rationale is:

1. For non-PR events (e.g., a push), CORE_REPO_SHA defaults to "main".

2. For PRs:

• If there’s a label named release, use the PR’s head branch (e.g., opentelemetrybot/prepare-release-1.32.0-0.53b0)

• Else, if there’s a label named "patch-release", use the PR’s base branch (e.g., usually release/v1.32.x-0.53bx)

• Otherwise, use "main".

Since only people with write permission can use labels, we are safe here. The automation is basically telling opentelemetrybot to open the release PRs with labels and use the labels to set the correct environment variable for CORE_REPO_SHA or CORE_CONTRIB_REPO_SHA.

I tested it locally using act, with the following event and checked tox is using the correct value for installing packages:

{
    "pull_request": {
      "labels": [
        {
          "name": "release"
        }
      ],
    "head": {
      "ref": "release/v1.32.x-0.53bx"
    },
    "base": {
      "ref": "main"
    }
    }
  }

and:

act -P ubuntu-latest=catthehacker/ubuntu:act-latest pull_request -W .github/workflows/misc_0.yml --container-architecture linux/amd64 -e event.json

Testing the behaviour from release workflows is hard, so I'm open to suggestions in terms of how testing it.

[aabmass]

Thanks! Makes sense to me but would like someone else to double check it

[xrmx]

The manual process is something like this atm:

• run the prepare workflow
• update the sha of the other repo to the same branch (opentelemetrybot/prepare-release...) to have green tests
• Release
• Update sha reference to the release/vX.Y.Z branch for patch releases or main for normal releases

With automation it should be something like:

• run the prepare workflow
• update the sha of the other repo to the release/vX.Y.Z branch for patch releases or main for normal releases to have green tests
• add label and have the workflow override the value set in the workflows
• release