chore: update changelog to include CVE-2025-66471 fix (#551)

*Description of changes:*
Manually adding CVE fix to changelog for release. There is no associated
PR since `urllib3` will auto-bump with a new release.


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Author: yiyuan-he

CHANGELOG.md

@@ -17,6 +17,7 @@ If your change does not need a CHANGELOG entry, add the "skip changelog" label t
   ([#547](https://github.com/aws-observability/aws-otel-python-instrumentation/pull/547))
 - Add Service and Environment dimensions to EMF metrics when Application Signals EMF export is enabled
   ([#548](https://github.com/aws-observability/aws-otel-python-instrumentation/pull/548))
+- Fix CVE-2025-66471. No associated PR since `urllib3` dependency will auto-bump to `2.6.x` upon release.
 
 ## v0.14.0 - 2025-11-19
 - Add Resource and CFN Attributes for Bedrock AgentCore spans