Automated Changelog Entry for 0.6.4 on main (#235)

Co-authored-by: GitHub Action <41898282+github-actions[bot]@users.noreply.github.com>

Author: davidbrochart

CHANGELOG.md

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 <!-- <START NEW CHANGELOG ENTRY> -->
 
+## 0.6.4
+
+([Full Changelog](https://github.com/jupyter/nbclient/compare/v0.6.3...01465b8d8597efa81f54f713ad3944fe963ab453))
+
+### Merged PRs
+
+- Make sure kernel is cleaned up in case an error occurred while starting kernel client [#234](https://github.com/jupyter/nbclient/pull/234) ([@CiprianAnton](https://github.com/CiprianAnton))
+- Suppress most warnings in tests [#232](https://github.com/jupyter/nbclient/pull/232) ([@davidbrochart](https://github.com/davidbrochart))
+
+### Contributors to this release
+
+([GitHub contributors page for this release](https://github.com/jupyter/nbclient/graphs/contributors?from=2022-05-09&to=2022-05-31&type=c))
+
+[@CiprianAnton](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3ACiprianAnton+updated%3A2022-05-09..2022-05-31&type=Issues) | [@davidbrochart](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3Adavidbrochart+updated%3A2022-05-09..2022-05-31&type=Issues)
+
+<!-- <END NEW CHANGELOG ENTRY> -->
+
 ## 0.6.3
 
 ([Full Changelog](https://github.com/jupyter/nbclient/compare/v0.6.2...61d36ce423b00231833c737f59041f33d72a7bb3))
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 [@blink1073](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3Ablink1073+updated%3A2022-05-03..2022-05-09&type=Issues) | [@chrisjsewell](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3Achrisjsewell+updated%3A2022-05-03..2022-05-09&type=Issues) | [@davidbrochart](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3Adavidbrochart+updated%3A2022-05-03..2022-05-09&type=Issues) | [@meeseeksmachine](https://github.com/search?q=repo%3Ajupyter%2Fnbclient+involves%3Ameeseeksmachine+updated%3A2022-05-03..2022-05-09&type=Issues)
 
-<!-- <END NEW CHANGELOG ENTRY> -->
-
 ## 0.6.2
 
 ([Full Changelog](https://github.com/jupyter/nbclient/compare/v0.6.1...bd36f50a299fb2e0656386ec487c2bbc67a9a1c4))