Call out fixed security vulnerabilities (#28400)

* Call out fixed security vulnerabilities

These will get automatically picked up when we pick up the new `python:3.XX-bullseye` images which have upgraded their debian versions already (for example https://hub.docker.com/layers/library/python/3.9-bullseye/images/sha256-d7e28b2648cb4611a94f068d92a236e7faaf6edb7589e01c09c1c16035c26d0a?context=explore has debian/aom 1.0.0.errata1-3+deb11u1 which has the fix). I confirmed that all 4 versions 3.<8, 9, 10, and 11> have the fix.

* Add to blog

CHANGES.md

@@ -83,7 +83,7 @@
 * Fixed X (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
 
 ## Security Fixes
-* Fixed (CVE-YYYY-NNNN)[https://www.cve.org/CVERecord?id=CVE-YYYY-NNNN] (Java/Python/Go) ([#X](https://github.com/apache/beam/issues/X)).
+* Python containers updated, fixing [CVE-2021-30474](https://nvd.nist.gov/vuln/detail/CVE-2021-30474), [CVE-2021-30475](https://nvd.nist.gov/vuln/detail/CVE-2021-30475), [CVE-2021-30473](https://nvd.nist.gov/vuln/detail/CVE-2021-30473), [CVE-2020-36133](https://nvd.nist.gov/vuln/detail/CVE-2020-36133), [CVE-2020-36131](https://nvd.nist.gov/vuln/detail/CVE-2020-36131), [CVE-2020-36130](https://nvd.nist.gov/vuln/detail/CVE-2020-36130), and [CVE-2020-36135](https://nvd.nist.gov/vuln/detail/CVE-2020-36135)
 
 ## Known Issues
 
@@ -146,6 +146,7 @@
 
 * Long-running Python pipelines might experience a memory leak: [#28246](https://github.com/apache/beam/issues/28246).
 * Python Pipelines using BigQuery IO or `orjson` dependency might experience segmentation faults or get stuck: [#28318](https://github.com/apache/beam/issues/28318).
+* Beam Python containers rely on a version of Debian/aom that has several security vulnerabilities: [CVE-2021-30474](https://nvd.nist.gov/vuln/detail/CVE-2021-30474), [CVE-2021-30475](https://nvd.nist.gov/vuln/detail/CVE-2021-30475), [CVE-2021-30473](https://nvd.nist.gov/vuln/detail/CVE-2021-30473), [CVE-2020-36133](https://nvd.nist.gov/vuln/detail/CVE-2020-36133), [CVE-2020-36131](https://nvd.nist.gov/vuln/detail/CVE-2020-36131), [CVE-2020-36130](https://nvd.nist.gov/vuln/detail/CVE-2020-36130), and [CVE-2020-36135](https://nvd.nist.gov/vuln/detail/CVE-2020-36135)
 
 
 # [2.49.0] - 2023-07-17

website/www/site/content/en/blog/beam-2.50.0.md

@@ -77,6 +77,7 @@ For more information on changes in 2.50.0, check out the [detailed release notes
 
 * Fixed DirectRunner bug in Python SDK where GroupByKey gets empty PCollection and fails when pipeline option `direct_num_workers!=1`.([#27373](https://github.com/apache/beam/pull/27373))
 * Fixed BigQuery I/O bug when estimating size on queries that utilize row-level security ([#27474](https://github.com/apache/beam/pull/27474))
+* Beam Python containers rely on a version of Debian/aom that has several security vulnerabilities: [CVE-2021-30474](https://nvd.nist.gov/vuln/detail/CVE-2021-30474), [CVE-2021-30475](https://nvd.nist.gov/vuln/detail/CVE-2021-30475), [CVE-2021-30473](https://nvd.nist.gov/vuln/detail/CVE-2021-30473), [CVE-2020-36133](https://nvd.nist.gov/vuln/detail/CVE-2020-36133), [CVE-2020-36131](https://nvd.nist.gov/vuln/detail/CVE-2020-36131), [CVE-2020-36130](https://nvd.nist.gov/vuln/detail/CVE-2020-36130), and [CVE-2020-36135](https://nvd.nist.gov/vuln/detail/CVE-2020-36135).
 
 ## Known Issues