feat(toolchains): update CPython 3.15.0 from rc2 to rc3 (#4220)

Make CPython 3.15.0rc3 available from the 20261003
python-build-standalone release.

Replace the 3.15.0rc2 runtime entries in the manifest with 3.15.0rc3
and update the default 3.15 minor version mapping.

(cherry picked from commit 87b8ae6f3583080dae252b4e385b4ca162fc638e)

Work towards #4224

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c51aef2..a008107 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,17 @@
 directory, or view the [latest generated
 changelog](https://rules-python.readthedocs.io/en/latest/changelog.html).
 
+{#v2-4-1}
+## [2.4.1] - 2026-10-05
+
+[2.4.1]: https://github.com/bazel-contrib/rules_python/releases/tag/2.4.1
+
+{#v2-4-1-changed}
+### Changed
+* (toolchain) Updated default Python 3.15 runtime from `3.15.0rc2` to
+  `3.15.0rc3`.
+
+
 {#v2-4-0}
 ## [2.4.0] - 2026-09-22
 

python/private/runtimes_manifest.txt

diff --git a/python/private/runtimes_manifest.txt b/python/private/runtimes_manifest.txt
index 493e0b8..0e54dcd 100755
--- a/python/private/runtimes_manifest.txt
+++ b/python/private/runtimes_manifest.txt
@@ -607,31 +607,31 @@
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python/private/runtimes_manifest_workspace.bzl

diff --git a/python/private/runtimes_manifest_workspace.bzl b/python/private/runtimes_manifest_workspace.bzl
index 69e55dd..9125535 100644
--- a/python/private/runtimes_manifest_workspace.bzl
+++ b/python/private/runtimes_manifest_workspace.bzl
@@ -618,32 +618,32 @@
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 """

python/versions.bzl

diff --git a/python/versions.bzl b/python/versions.bzl
index f238f06..f7afa95 100644
--- a/python/versions.bzl
+++ b/python/versions.bzl
@@ -49,7 +49,7 @@
     "3.12": "3.12.13",
     "3.13": "3.13.13",
     "3.14": "3.14.4",
-    "3.15": "3.15.0rc2",
+    "3.15": "3.15.0rc3",
 }
 
 def _generate_platforms():

tests/support/mocks/python_ext.bzl

diff --git a/tests/support/mocks/python_ext.bzl b/tests/support/mocks/python_ext.bzl
index 87d492c..7c1ac7b 100644
--- a/tests/support/mocks/python_ext.bzl
+++ b/tests/support/mocks/python_ext.bzl
@@ -111,7 +111,7 @@
 9999999999999999999999999999999999999999999999999999999999999999  20241016/cpython-3.13.0+20241016-x86_64-unknown-linux-gnu-install_only.tar.gz
 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa  20260414/cpython-3.14.4+20260414-x86_64-unknown-linux-gnu-install_only.tar.gz
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-cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc  20260929/cpython-3.15.0rc2+20260929-x86_64-unknown-linux-gnu-install_only.tar.gz
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 dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd  20241205/cpython-3.13.1+20241205-x86_64-unknown-linux-gnu-install_only.tar.gz
 """