docs: v2.9.1 changelog

Author: kozistr

docs/changelogs/v2.9.1.md

@@ -4,7 +4,6 @@
 
 * fix weight decay in Ranger21 (#170)
 
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 ## Diff
 
 [2.9.0...2.9.1](https://github.com/kozistr/pytorch_optimizer/compare/v2.9.0...v2.9.1)