pw_presubmit: Convert strs to Paths
pw_presubmit: Convert strs to Paths

Convert strings from the --list-steps-file argument to Path objects.

Bug: b/256007641
Change-Id: I71435ced9f1a001fc1e7df8cb6fa530a9c182e94
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/117910
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Jonathan Cardy <b541952bb80ecc8bd0f16a279d10badd687d1513@google.com>
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>

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