Fix changelog parsing

[nwithan8]

Fixed and commented changelog parsing for CI.

Initial comment in skipped "big header" section was causing a key error issue.

Closes #770

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov]

Codecov Report

Merging #781 (dfd4527) into master (4ae2ffe) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #781   +/-   ##
=======================================
  Coverage   21.51%   21.51%           
=======================================
  Files          63       63           
  Lines        8542     8542           
  Branches     1572     1572           
=======================================
  Hits         1838     1838           
  Misses       6680     6680           
  Partials       24       24           

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[oddstr13]

If I'm reading this right, it silently drops changes that don't have proper section tags set, which is undesirable.

Changes that shouldn't be included are explicitly tagged as so (and don't show up here), and the presence of an uncategorized PR here is an oversight and should preferably be corrected before making a release.

For now, I think the best way to handle this here is to create a default initial section where the problematic PRs go.

---

I intend to simplify the release workflow (at the cost of some complexity in the gh actions), same as I recently did in jprm, which would have the bump release PR continually created and updated (with the content created here), but that's out of scope for this particular PR.