Update release documentation with v3 instructions

CONTRIBUTING.md

@@ -57,18 +57,14 @@ Here are a few things you can do that will increase the likelihood of your pull
 ## Releasing (write access required)
 
 1. The first step of releasing a new version of the `codeql-action` is running the "Update release branch" workflow.
-    This workflow goes through the pull requests that have been merged to `main` since the last release, creates a changelog, then opens a pull request to merge the changes since the last release into the `releases/v2` release branch.
+    This workflow goes through the pull requests that have been merged to `main` since the last release, creates a changelog, then opens a pull request to merge the changes since the last release into the `releases/v3` release branch.
 
     You can start a release by triggering this workflow via [workflow dispatch](https://github.com/github/codeql-action/actions/workflows/update-release-branch.yml).
-1. The workflow run will open a pull request titled "Merge main into releases/v2". Mark the pull request as [ready for review](https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request#marking-a-pull-request-as-ready-for-review) to trigger the PR checks.
-1. Review the checklist items in the pull request description.
-    Once you've checked off all but the last two of these, approve the PR and automerge it.
-1. When the "Merge main into releases/v2" pull request is merged into the `releases/v2` branch, the "Tag release and merge back" workflow will create a mergeback PR.
-    This mergeback incorporates the changelog updates into `main`, tags the release using the merge commit of the "Merge main into releases/v2" pull request, and bumps the patch version of the CodeQL Action.
+1. The workflow run will open a pull request titled "Merge main into releases/v3". Follow the steps on the checklist in the pull request. Once you've checked off all but the last two of these, approve the PR and automerge it.
+1. When the "Merge main into releases/v3" pull request is merged into the `releases/v3` branch, a mergeback pull request to `main` and a backport pull request to `releases/v2` will both be automatically created. This mergeback pull request incorporates the changelog updates into `main`, tags the release using the merge commit of the "Merge main into releases/v3" pull request, and bumps the patch version of the CodeQL Action. The backport pull request will incorporate the updates into `releases/v2`.
+1. Approve the mergeback and backport pull requests and automerge them.
 
-    Approve the mergeback PR and automerge it.
-
-Once the mergeback has been merged to `main`, the release is complete.
+Once the mergeback and backport pull request have been merged, the release is complete.
 
 ## Keeping the PR checks up to date (admin access required)