Fix arrow libraries from download & build not being found in some cases

[Wumpf]

What

Apparently they don't always end up in /lib depending on how cmake was configured. This should fix this!

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

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[02alexander]

Looks good! Fixed the issue for me.