chore(gevent): add release note for gevent mitigation (backport #4268) (#4269)

This is an automatic backport of pull request #4268 done by [Mergify](https://mergify.com).


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Author: mergify[bot]

releasenotes/notes/mitigate-1-5-gevent-regression-c505053014036c6a.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    gevent: disable gevent after fork hook which could result in a performance regression.