hevm: fix prove tests for latest ds-test

[d-xo]

Since https://github.com/dapphub/ds-test/pull/30 calls to failed() can contain reverting branches due to the call into abi.decode().

This meant that using prove tests with the latest ds-test version would always fail with a hard error.

This change updates the symbolic test stepper to correctly report bailed as true for branches that reverted during the call to failed().

Description

Checklist

• [x] tested locally
• [ ] added automated tests
• [ ] updated the docs
• [x] updated the changelog