address comments

.ci/thin_macos_qtlib.sh

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+#!/bin/bash
+
+# The macos binaries from aqt are fat (universal), so we thin them to the target architecture to reduce the size of
+# the packages and caches using lipo.
+
+# This script is meant to be used by the ci enironment on macos runners only.
+# It uses the runner's GITHUB_WORKSPACE env variable.
+arch=$(uname -m)
+nproc=$(sysctl -n hw.ncpu)
+
+function thin() {
+  local libfile=$0
+  if file -b --mime-type "$libfile" | grep -q "application/x-mach-binary"; then
+    echo "Processing $libfile"
+    lipo "$libfile" -thin "$arch" -output "$libfile"
+  fi
+  return 0
+}
+export -f thin  # export to allow use in xargs
+
+echo "::group::Thinning Qt libraries to $arch using $nproc cores"
+find "$GITHUB_WORKSPACE/Qt" -type f -print0 | xargs -0 -n1 -P"$nproc" -I{} bash -c "thin '{}'"
+echo "::endgroup::"