[ci] Specify if-no-files-found on actions/upload-artifact@v4 (#32679)

Defaults to warn, but since some steps require these artifacts to be
uploaded we specify an error if its not found. Some other steps like
playwright test-results are only uploaded on failure so it's okay to
ignore.
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[//]: # (BEGIN SAPLING FOOTER)
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* #32680
* __->__ #32679
* #32678