release: Release cloud_events 0.8.0 (was 0.7.1)

[github-actions]

This pull request prepares new releases for the following components:

• cloud_events 0.8.0 (was 0.7.1)

For each releasable component, this pull request modifies the version and provides an initial changelog entry based on conventional commit messages. You can edit these changes before merging, to release a different version or to alter the changelog text.

• To confirm this release, merge this pull request, ensuring the "release: pending" label is set. The release script will trigger automatically on merge.
• To abort this release, close this pull request without merging.

The generated changelog entries have been copied below:

---

cloud_events

• BREAKING CHANGE: Raise AttributeError if an illegal attribute name is used
• ADDED: Require Ruby 2.7 or later
• FIXED: Improved hashing algorithm for opaque event objects
• FIXED: Removed dependency on base64 gem
• FIXED: Raise AttributeError if an illegal attribute name is used
• DOCS: Add link to the security mailing list

[github-actions]

Release PR closed without merging.