[5.8] tsan-ignores-arc-locks.swift: post process test binary on Darwin (#66347)
This allows the `DYLD_LIBRARY_PATH` override to work as expected and
avoid crashes when running.
*Scope:* change in a Swift validation test
*Issue:* rdar://110272889
*Risk:* Low -- other standard library tests are already using the same post process step
*Testing:* execute the toolchain PR job to exercise this test
(cherry picked from commit 44a40979e52be8e9344b8ca6069614a29aeff6cd,
#66308)