Fix markdown list indentation in notes2news.pl script

[coderabbitai]

Problem

The NEWS.md file generated by the notes2news.pl script contains inconsistent markdown list indentation that violates markdownlint rule MD007.

Markdownlint Violations

Multiple lines in NEWS.md (lines 377-417) show indentation errors:

• Expected: 2 spaces for nested bullets
• Actual: 4 spaces for nested bullets

Example violations:

377-377: Unordered list indentation - Expected: 2; Actual: 4 (MD007)
381-381: Unordered list indentation - Expected: 2; Actual: 4 (MD007)
382-382: Unordered list indentation - Expected: 2; Actual: 4 (MD007)

Root Cause

If NEWS.md is generated by the notes2news.pl script, then the script needs to be updated to emit consistent 2-space indentation for nested markdown list items.

Solution

Modify notes2news.pl to:

1. Use 2-space indentation for each nested level in markdown lists
2. Ensure sub-bullets under top-level bullets are prefixed with exactly two spaces
3. Maintain consistency across all generated markdown content

Reference

This issue was identified in PR #2970: #2970 (comment)

Acceptance Criteria

• notes2news.pl script updated to use 2-space markdown list indentation
• Generated NEWS.md passes markdownlint MD007 rule
• All nested bullets consistently use 2-space increments