use paketobuildpacks for custom builder validation

[glasnt]

Cloud Run button supports supplying a custom builder, rather than using the default "gcr.io/buildpacks/builder".

The buildpacks-builder test was failing due to Heroku buildpacks no longer having a tagged latest (presumably this worked before), and have also have been deprecated, replaced with heroku/builder. However, both of these versions are not compatible with the version of pack being used (e.g.ERROR: failed to build: Builder 'heroku/builder:22' is incompatible with this version of pack)

So instead, replace the use of heroku with another buildpack. From the pack builder suggest output, paketobuildpacks/builder is an option. Using the :full image since the sample application used is PHP, and the :tiny version doesn't support this.

[jamesward]

Thanks @glasnt! Can you see why the integration test is failing? I don't have access to the GCP project for it.

[glasnt]

Just granted you access, see emails.
The integration tests run against the master branch tests, just fired a manual test using the tests from this branch.

[jamesward]

I think the integration test is failing because it is fetching the master branch for the tests instead of the branch the PR is on:

Command './cloudshell_open --repo_url=https://github.com/GoogleCloudPlatform/cloud-run-button --git_branch=master --dir=tests/buildpacks-builder' returned 1

The actual error is:

ERROR: failed to build: failed to fetch builder image 'index.docker.io/heroku/buildpacks:latest': image 'index.docker.io/heroku/buildpacks:latest' does not exist on the daemon: not found

So I think this PR fixes things but just isn't being fetched to test the fix. If that sounds right we can just merge this.

[glasnt]

Correct: the integration test only works for non-testing related changes. I've setup a separate Cloud Build trigger to allow customisation of the branch where tests are sourced from (integration-tests-MANUAL).

You should have access to those test results to verify the change: https://github.com/GoogleCloudPlatform/cloud-run-button/pull/246/checks?check_run_id=19266836330

[jamesward]

Awesome. Thanks @glasnt!