branch-number override of section numbering: https://github.com/metan…

[opoudjis]

…orma/metanorma-iso/issues/1044

Metanorma PR checklist

• [x] Breaking changes (list related PRs) : https://github.com/metanorma/isodoc/pull/544
• [ ] Documentation update required (create task for this)
• [ ] External dependency introduced (documentation update need)
• [ ] Gem with native library introduced

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (4549781) 95.51% compared to head (9c44a10) 95.50%.

Files	Patch %	Lines
lib/isodoc/itu/xref_section.rb	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #477 +/- ## ========================================== - Coverage 95.51% 95.50% -0.01% ========================================== Files 26 26 Lines 1427 1424 -3 ========================================== - Hits 1363 1360 -3 Misses 64 64 ```

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