Hotfix unbound `$PY` variable breaking cargo script (#11209)
Hotfix unbound `$PY` variable breaking cargo script (#11209)

If `set -u` is configured, then it errors that `$PY` is not set.

[ci skip-rust]
[ci skip-build-wheels]
pantsbuild/pants,jsirois/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,jsirois/pants,benjyw/pants,benjyw/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,jsirois/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants