changelog: add note abot DHE-RSA removal

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/ChangeLog.d/9685.txt b/ChangeLog.d/9685.txt
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index 0000000..9820aff
--- /dev/null
+++ b/ChangeLog.d/9685.txt
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+Removals
+   * Remove support for the DHE-RSA key exchange in TLS 1.2.