Publish Buildkite Packages — Fix Urls

[sj26]

Continuing from #2824, it's now failing with a "not found":

I found the matching trace in Datadog APM:

https://app.datadoghq.com/apm/trace/1355574743850893837

which revealed the request path was:

/v2/packages/organizations/buildkite/agent-rpm-experimental/registries/buildkite/agent-rpm-experimental/packages

The problem is the organization and registry slug weren't being split up quite right. The glob was the wrong way around 🤦

Given:

REGISTRY="acme-inc/widgets"

Before:

ORGANIZATION_SLUG="${REGISTRY%*/}"
# => ORGANIZATION_SLUG=acme-inc/widgets

REGISTRY_SLUG="${REGISTRY#/*}"
# => REGISTRY_SLUG=acme-inc/widgets

After:

ORGANIZATION_SLUG="${REGISTRY%/*}"
# => ORGANIZATION_SLUG=acme-inc

REGISTRY_SLUG="${REGISTRY#*/}"
# => REGISTRY_SLUG=widgets

(I swear I tested these to check they were the right way around, but clearly have done something silly along the way.)

I've also adjusted the curl command to exit non-zero on HTTP error codes, so the step wouldn't have been green in this case or for any future errors.