fix: build on main and nightly (#1280)

- Fixes issue with nightly builds where `filter_builds` wasn't being
applied without `eval_target` being supplied. Closes #1265
- Fix demonstrated
[here](https://github.com/unionlabs/union/actions/runs/7786460547/job/21231418919)
- Fixes issue where build summaries triggered an error if there were no
jobs queued (closes #1261 )
- Fix demonstrated
[here](https://github.com/unionlabs/union/actions/runs/7788142685)
  
Needs unionlabs/workflows#29