PR_REQUEST_TEMPLATE: add hyphen character before tick box

[CleanMachine1]

Signed-off-by: CleanMachine1 78213164+CleanMachine1@users.noreply.github.com

Thank you for your contribution to the Pi-hole Community!

Please read the comments below to help us consider your Pull Request.

We are all volunteers and completing the process outlined will help us review your commits quicker.

Please make sure you

1. Base your code and PRs against the repositories developmental branch.
2. Sign Off all commits as we enforce the DCO for all contributions

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• What does this PR aim to accomplish?:

This solves a very minor issue with all checkboxes not being registered as checkboxes.

• How does this PR accomplish the above?:

Fixing the markdown.

• What documentation changes (if any) are needed to support this PR?:

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By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

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• [x] I have read the above and my PR is ready for review. Check this box to confirm

[dschaper]

Thanks!