update changelog

docs/docs/changelog.mdx

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 <!-- TOWNCRIER -->
 
+## [3.6.15] - 2023-11-30
+
+Rasa 3.6.15 (2023-11-30)                         
+### Bugfixes
+- [#12965](https://github.com/rasahq/rasa/issues/12965): Fixed connection timeout to action server by setting `KEEP_ALIVE_TIMEOUT` to `120`, and reverting changes introduced in [#12886](https://github.com/rasahq/rasa/issues/12886).
+
+
+## [3.6.14] - 2023-11-17
+
+Rasa 3.6.14 (2023-11-17)                         
+### Bugfixes
+- [#12948](https://github.com/rasahq/rasa/issues/12948): Fixed UnexpecTEDIntentlessPolicy training errors that resulted from a change to batching behavior. Changed the batching behavior back to the original for all components. Made the changed batching behavior accessible in DietClassifier using `drop_small_last_batch: True`.
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+
 ## [3.6.13] - 2023-10-23
 
 Rasa 3.6.13 (2023-10-23)