update changelog

Author: rcannood

CHANGELOG.md

@@ -1,6 +1,9 @@
 # task_spatial_simulators dev
 
 Bug fixes:
+  - `splatter`, `zinbwave` and `symsim`: drop a self-referential `match()`
+    reorder that could only ever return `1:n`.
+  - `downstream`: drop the unused `plat` mock argument.
   - `run_benchmark`: raise `uns_length_cutoff` from 15 to 50, so that
     `extract_uns_metadata` no longer drops the `metric_ids` of components that
     emit more than 15 metrics. All 28 `ks_statistic_gene_cell` metrics were