Ignore forks

[laurentsenta]

Thanks for sharing and maintaining this action,

I have a workflow that downloads a bunch of outputs from other repositories.

For example, I select the master branch from ipfs/kubo.

My action failed with:
https://github.com/ipfs/gateway-conformance/actions/runs/6218823800/job/16875980114

Run dawidd6/action-download-artifact@v2
==> Repository: ipfs/kubo
==> Artifact name: gateway-conformance.json
==> Local path: ./
==> Workflow name: gateway-conformance.yml
==> Workflow conclusion: completed
==> Branch: master
==> (found) Run ID: 62[1](https://github.com/ipfs/gateway-conformance/actions/runs/6218823800/job/16875980114#step:3:1)0849710
==> (found) Run date: 2023-09-[17](https://github.com/ipfs/gateway-conformance/actions/runs/6218823800/job/16875980114#step:3:18)T01:42:28Z
==> (not found) Artifact: gateway-conformance.json
==> Found the following artifacts instead:
Error: no artifacts found

When I open the run
it's a run from the master branch of a fork. Which is not what I want to do.
A fork could poison my workflow's output.

Related: ipfs/gateway-conformance#167