Fixed broken link in PR template

[olineumann]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?
• If you made a notable change (that affects users), did you update the CHANGELOG?

What does this PR do?

CHANGELOG.md link in PR template pointed to Error 404 Page from GitHub. It could be confusing for new users who make their first PR.

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

Merging #1675 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #1675   +/-   ##
======================================
  Coverage      88%     88%           
======================================
  Files          71      71           
  Lines        4175    4175           
======================================
  Hits         3692    3692           
  Misses        483     483