Add exact-match arg to git describe call

[JordanMartinez]

Description of the change

Fixes #1078

Checklist:

• Added the change to the "Unreleased" section of the changelog
• Added some example of the new feature to the README
• Added a test for the contribution (if applicable)

P.S.: the above checks are not compulsory to get a change merged, so you may skip them. However, taking care of them will result in less work for the maintainers and will be much appreciated 😊

[f-f]

Did you see the Windows CI failure?

[JordanMartinez]

I did. But since the changes here don't add any test code, and the other builds passed, which means the PureScript code compiled fine, I assumed it was a flaky windows test and merged it.
I restarted the windows build here just in case and it succeeded this time.