util: Filter out macOS process serial number

Summary: This is a backport of core#17184

Test Plan:
I don't have a MacOS to test this. This should be trivial enough a change to simply check that it doesn't break regular CI builds and a standard local build.
ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9901