build_RootFilesystemSize failures on Glimmer

Started happening between R54-8743.62.0 and R54-8743.64.0 across multiple hosts.  Happens every time.

e.g. https://uberchromeos-server38.corp.google.com/new_tko/#tab_id=test_detail_view&object_id=369721404

https://wmatrix.googleplex.com/platform/unfiltered?platforms=glimmer&tests=build_RootFilesystemSize&days_back=30&releases=54&hide_missing=True


Diffs:
https://chromium.googlesource.com/chromium/src/+log/54.0.2840.58..54.0.2840.59?pretty=fuller&n=10000
https://crosland.corp.google.com/log/8743.62.0..8743.64.0