PYTHON-5272 Expand changelog entry with per-case caching details

Author: blink1073

doc/changelog.rst

@@ -7,7 +7,7 @@ Changes in Version 4.18.0
 - Improved TLS connection performance by reusing TLS sessions across connections
   to the same server, avoiding a full handshake on each new connection.
   Session reuse is active on the sync path unconditionally, and on the async
-  path when running Python 3.11 or later.
+  path on Python 3.11 or later.
 
 Changes in Version 4.17.0 (2026/04/20)
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