gh-36632: .ci/merge-fixes.sh: Reduce output
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We suppress long output (https://github.com/sagemath/sage/actions/runs/6
738804468/job/18319117745?pr=36508#step:3:11) and scary-looking but
harmless error messages (https://github.com/sagemath/sage/actions/runs/6
738804468/job/18319117745?pr=36508#step:3:1114).
Example of a quieter run with this change: https://github.com/sagemath/s
age/actions/runs/6739070170/job/18319882833?pr=36632#step:3:19
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URL: https://github.com/sagemath/sage/pull/36632
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee
