Fix line breaks in PR template

[imjasonh]

Before this, the Reviewer Notes section reads a bit like beat poetry (see below 👇 ). 😹

(After this change)

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• [n] Includes tests (if functionality changed/added)
• [n] Includes docs (if user facing)
• [y] Commit messages follow commit message best practices

See the contribution guide for more details.

Double check this list of stuff that's easy to miss:

• If you are adding a new binary/image to the cmd dir, please update
  the release Task and TaskRun to build and release this image

Reviewer Notes

If API changes
are included, additive changes
must be approved by at least two OWNERS
and backwards incompatible changes
must be approved by more than 50% of the OWNERS,
and they must first be added
in a backwards compatible way.

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ImJasonH

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• OWNERS [ImJasonH]

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[dibyom]

I'll miss the beat poetry!

/lgtm