docs(changelog): add 2.3.4 entry for win32 Python runtimes

PR #4156 merged the win32 Python runtime additions directly to the
release/2.3 branch without a changelog update. Add the 2.3.4 release
section to CHANGELOG.md so the upcoming patch release documents the new
toolchains.

Work towards #4173

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1372b4b..ec48cd7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,15 @@
 directory, or view the [latest generated
 changelog](https://rules-python.readthedocs.io/en/latest/changelog.html).
 
+{#v2-3-4}
+## [2.3.4] - 2026-09-21
+[2.3.4]: https://github.com/bazel-contrib/rules_python/releases/tag/2.3.4
+{#v2-3-4-added}
+### Added
+* (toolchains) Added win32 (`i686-pc-windows-msvc`) Python runtimes for
+  versions 3.9.25, 3.10.20, 3.11.15, 3.12.13, 3.13.13, and 3.14.4
+  ([#4156](https://github.com/bazel-contrib/rules_python/pull/4156)).
+
 {#v2-3-3}
 ## [2.3.3] - 2026-09-02