fix(web-api): type Slack Lists message fieldFix Slack Lists message field response type responses

[cxdmnls]

Summary

Fixes #2598.

This PR updates the Slack Lists FieldMessage.message type to match the API response shape. The field can now be either a single message object or an array of message objects. A focused tsd type test was added to cover both response shapes.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[salesforce-cla]

Thanks for the contribution! Unfortunately we can't verify the commit author(s): 常侯鑫 <3***@q***.com>. One possible solution is to add that email to your GitHub account. Alternatively you can change your commits to another email and force push the change. After getting your commits associated with your GitHub account, sign the Salesforce Inc. Contributor License Agreement and this Pull Request will be revalidated.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 211c417

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR