Update changelog

Author: nspope

python/CHANGELOG.rst

@@ -7,6 +7,12 @@
 - ``TreeSequence.map_to_vcf_model`` now also returns the transformed positions and
   contig length. (:user:`benjeffery`, :pr:`XXXX`, :issue:`3173`)
 
+**Bugfixes**
+
+- Fix bug in `TreeSequence.pair_coalescence_counts` when `span_normalise=True`
+  and a window breakpoint falls within an internal missing interval.
+  (:user:`nspope`, :pr:`3176`, :issue:`3175`)
+
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 [0.6.4] - 2025-05-21
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