Improve error message when upstream-provider-org is required

[iwahbe]

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Issue details

Currently, when upstream-provider-org is missing (but should be present), the error looks like this:

-- failed ---
  - X Lookup Tag SHA: exit status 128:
remote: Repository not found.
fatal: repository 'https://github.com//terraform-provider-port-labs/' not found

When we are unable to find the upstream repo, we should fail with a clear and actionable error.

Affected area/feature