pw_env_setup: Fix alias check when 'set -e'
pw_env_setup: Fix alias check when 'set -e'

This suppresses the failure of 'alias python' when 'python' is not an
alias so it can run under 'set -e' without exiting early.

Change-Id: I879954cb42791de50e613e22e2dd2d4ed38336e0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/42140
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Reviewed-by: Janusz Sobczak <7d673ca4ae780ec22a4458087c3b10960a9a89ff@google.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed