CI - Multi-line runs fail properly on Windows

[bfops]

Description of Changes

It turns out that multi-line run statements don't fail properly on Windows. If one of the lines fails, the run won't exit early, and in fact the step will return successful.

API and ABI breaking changes

CI-only changes.

Expected complexity level and risk

1

Testing

• Confirmed that a one-line command will fail properly on Windows: https://github.com/clockworklabs/SpacetimeDB/actions/runs/18204663513/job/51831974918?pr=3337
• Confirmed that a multi-line command properly exits early with these changes: https://github.com/clockworklabs/SpacetimeDB/actions/runs/18203897520/job/51829384741?pr=3335
• Confirmed that a windows package build still works even though the shell is bash for part of it now (https://github.com/clockworklabs/SpacetimeDB/actions/runs/18205281236/job/51834045429)

[jdetter]

LGTM, thanks for investigating this Zeke 👍