fix: ensure Changelog ends on a newline

[muesli]

This ensures the Changelog ends with a trailing newline, regardless of a footer being set.

Also added tests to verify this behavior.

[vercel]

@muesli is attempting to deploy a commit to the Goreleaser Team on Vercel.

A member of the Team first needs to authorize it.

[codecov]

Codecov Report

Merging #1919 (541d5f0) into master (56f3493) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1919   +/-   ##
=======================================
  Coverage   81.72%   81.73%           
=======================================
  Files          73       73           
  Lines        3864     3866    +2     
=======================================
+ Hits         3158     3160    +2     
  Misses        580      580           
  Partials      126      126           

Impacted Files	Coverage Δ
internal/pipe/changelog/changelog.go	92.85% <100.00%> (+0.12%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 56f3493...541d5f0. Read the comment docs.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.