Remove script input from publish step in build.yaml. (#977)

Nightly tests failed because an extra `script` variable was passed to the wheel publish workflow.

Failures look like:
```
Invalid workflow file: .github/workflows/build.yaml#L65
The workflow is not valid. .github/workflows/build.yaml (Line: 65, Col: 15): Invalid input, script is not defined in the referenced workflow.
```

https://github.com/rapidsai/ucx-py/actions/runs/5664871243

Follow-up to #973.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Ray Douglass (https://github.com/raydouglass)

URL: #977

.github/workflows/build.yaml

@@ -62,4 +62,3 @@ jobs:
       sha: ${{ inputs.sha }}
       date: ${{ inputs.date }}
       package-name: ucx_py
-      script: ci/test_wheel.sh