Update changelog rewriting step to match v2+ only release notes

Author: henrymercer

.github/update-release-branch.py

@@ -286,7 +286,7 @@ def main():
     subprocess.run(['sed', '-i', 's/^## 2\./## 1./g', 'CHANGELOG.md'])
 
     # Remove changelog notes from v2 that don't apply to v1
-    subprocess.run(['sed', '-i', '/^- The CodeQL Action now runs on Node\.js v16\./d', 'CHANGELOG.md'])
+    subprocess.run(['sed', '-i', '/^- \[v2+ only\]/d', 'CHANGELOG.md'])
 
     # Amend the commit generated by `npm version` to update the CHANGELOG
     run_git('add', 'CHANGELOG.md')