release: bump wdl-engine to 0.8.1.

[peterhuene]

Before submitting this PR, please make sure:

For external contributors:

• You have read the CONTRIBUTING guide in its entirety.
• You have not used AI on any parts of this pull request.

For all contributors:

• You have added a few sentences describing the PR here.
• Your code builds clean without any errors or warnings.
• You have added tests (when appropriate).
• You have updated the README or other documentation to account for these
  changes (when appropriate).
• You have added an entry to the relevant CHANGELOG.md (see
  "keep a changelog" for more information).
• Your commit messages follow the conventional commit style.
• Your PR title follows the conventional commit style.

[a-frantz]

this needs to bump https://github.com/stjude-rust-labs/wdl/blob/main/wdl/Cargo.toml#L64 as well