Handle CHANGELOGs with "v" in the headings

[mattwynne]

🤔 What's the problem you're trying to solve?

We're not consistent about whether we use a "v" in the h2s in our CHANGELOGs

Example: https://github.com/cucumber/html-formatter/blob/main/CHANGELOG.md#1910---2022-04-15
Example: https://github.com/cucumber/multi_test/blob/main/CHANGELOG.md#v012

We should handle that, instead of doing this:

polyglot-release 1.0.0
No git tag found for vv0.1.2 (found in CHANGELOG.md)!

Do you need to run this?
    git fetch --tags

✨ What's your proposed solution?

I would like us to normalise the headings, only adding a prefix "v" if it's not already there. So we can handle both styles.

⛏ Have you considered any alternatives or workarounds?

Throw an error if the heading starts with a "v" and ask the user to clean up their CHANGELOG.

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