Skip post-processing of upgrade directories that fail to list

[lathanh]

Background

• Upgrade directories may be empty if the upgrade is invalid.
• In some cloud filesystems, there aren't actual directories (including for S3 and Google Cloud Storage). So, an "empty directory" means the directory doesn't exist and can't be listed.

Problem

Trying to list an "empty" upgrade directory during post-processing (which can happen if the upgrade was invalid) fails with an exception for Google Cloud Storage.

Fix

Treat a failure to list an upgrade directory during post-processing the same as when the directory is empty (i.e., skip it).

Alternatives considered

1. Create a fake directory: This causes the directory listing to also include the fake directory itself, causing a different error (trying to read the directory as if it's a parquet file), and thus a change to also list only parquet files in the directory (i.e., requires a hack to handle the hack).

Checklist

Not all may apply

• [x] Code changes (must work)
• [x] Tests exercising your feature/bug fix (check coverage report on Checks -> BuildStockBatch Tests -> Artifacts)
• [x] Coverage has increased or at least not decreased. Update minimum_coverage in .github/workflows/ci.yml as necessary.
• [x] All other unit and integration tests passing
• [x] Update validation for project config yaml file changes
• [x] Update existing documentation
• [x] Run a small batch run on Eagle to make sure it all works if you made changes that will affect Eagle
• [x] Add to the changelog_dev.rst file and propose migration text in the pull request

[github-actions[bot]]

File	Coverage
All files	85%	:white_check_mark:
base.py	90%	:white_check_mark:
eagle.py	77%	:white_check_mark:
exc.py	57%	:white_check_mark:
local.py	70%	:white_check_mark:
postprocessing.py	84%	:white_check_mark:
utils.py	91%	:white_check_mark:
cloud/docker_base.py	0%	:x:
sampler/base.py	79%	:white_check_mark:
sampler/downselect.py	33%	:white_check_mark:
sampler/precomputed.py	93%	:white_check_mark:
sampler/residential_quota.py	61%	:white_check_mark:
test/test_docker.py	33%	:white_check_mark:
test/test_validation.py	97%	:white_check_mark:
workflow_generator/base.py	90%	:white_check_mark:
workflow_generator/commercial.py	53%	:white_check_mark:
workflow_generator/residential_hpxml.py	86%	:white_check_mark:

Minimum allowed coverage is 33%

Generated by :monkey: cobertura-action against 15036e1c8d0d43e42f042cd60a82c23f0af717e2

[lathanh]

Like in the other PR, I added the checklist from our PR template (which should be working right again). It helps me to make sure we've sorted all things that can come up. If something doesn't apply to this PR, just ~cross it out~ and check the box.

Done! Let me know if there's anything else.