Fixes the use of release when generating issue title

Related to #54 (closed)

The switching back and forth between using a Hash or String to represent the release has been causing the pipeline to fail for various reasons. The latest failure (https://gitlab.com/gitlab-org/async-retrospectives/-/pipelines/759146561) is another example of that.

This change uses only the release title to generate the title of the issue. Using the whole release Hash is unintentional and, even if it didn't exceed the 255 character limit, would cause unwieldy and unreadable issue titles.

Also added is a test to ensure this doesn't get accidentally changed back to a string in future or, if it does, the title is still generated as expected.