Update changelog.

CHANGES.txt

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 lxml changelog
 ==============
 
+5.2.0 (2024-??-??)
+==================
+
+Other changes
+-------------
+
+* LP#1958539: The ``lxml.html.clean`` implementation suffered from several (only if used)
+  security issues in the past and was now extracted into a separate library:
+
+  https://github.com/fedora-python/lxml_html_clean
+
+  Projects that use lxml without "lxml.html.clean" will not notice any difference,
+  except that they won't have potentially vulnerable code installed.
+  The module is available as an "extra" setuptools dependency "lxml[html_clean]",
+  so that Projects that need "lxml.html.clean" will need to switch their requirements
+  from "lxml" to "lxml[html_clean]", or install the new library themselves.
+
+* The minimum CPU architecture for the Linux x86 binary wheels was upgraded to
+  "sandybridge" (launched 2011), and glibc 2.28 / gcc 12 (manylinux_2_28) wheels were added.
+
+
 5.1.1 (2024-03-28)
 ==================