update-pipeline.sh script is not working for v2

[dmikusa]

Expected Behavior

When the update pipeline job runs, it sets the .github/pipeline-version file to the version of pipeline-builder that was used. It incorrectly selects the version for v2.

Current Behavior

It uses gh api to fetch the latest release, and uses the version number of the latest release. This is not accurate because what is the latest release is not tied to the code that has been checked out and is running.

Possible Solution

Look at the checked out branch and determine the version that way, like compute-version.sh.

Steps to Reproduce

paketo-buildpacks/pipeline-builder-stool-pigeon#4

Motivations

It should display accurate version information.