Fix regression introduced by #610

[znichollscr]

Description

Fixes #648

Checklist

• Make sure changes are covered by existing or new tests.
• For at least one Python version, make sure test pass on your local environment.
• Create a file in src/towncrier/newsfragments/. Briefly describe your
  changes, with information useful to end users. Your change will be included in the public release notes.
• Make sure all GitHub Actions checks are green (they are automatically checking all of the above).
• Ensure docs/tutorial.rst is still up-to-date.
  * [ ] If you add new CLI arguments (or change the meaning of existing ones), make sure docs/cli.rst reflects those changes.
• If you add new configuration options (or change the meaning of existing ones), make sure docs/configuration.rst reflects those changes.

[adiroiban]

Thanks. Changes looks good.

I am looking at the Markdown tutorial documentation at https://towncrier.readthedocs.io/en/latest/markdown.html

and I can see that it has this config

title_format = "## [{version}](https://github.com/twisted/my-project/tree/{version}) - {project_date}"

so it looks like #610 is a bug.

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Thanks again.

[speedenator]

fixed while I slept. Love it! Thanks @znichollscr and @adiroiban !