Set version to 6.3.3

Author: bdarnell

docs/releases.rst

@@ -4,6 +4,7 @@ Release notes
 .. toctree::
    :maxdepth: 2
 
+   releases/v6.3.3
    releases/v6.3.2
    releases/v6.3.1
    releases/v6.3.0

docs/releases/v6.3.3.rst

@@ -0,0 +1,12 @@
+What's new in Tornado 6.3.3
+===========================
+
+Aug 11, 2023
+------------
+
+Security improvements
+~~~~~~~~~~~~~~~~~~~~~
+
+- The ``Content-Length`` header and ``chunked`` ``Transfer-Encoding`` sizes are now parsed
+  more strictly (according to the relevant RFCs) to avoid potential request-smuggling
+  vulnerabilities when deployed behind certain proxies.

tornado/__init__.py

@@ -22,8 +22,8 @@
 # is zero for an official release, positive for a development branch,
 # or negative for a release candidate or beta (after the base version
 # number has been incremented)
-version = "6.3.2"
-version_info = (6, 3, 2, 0)
+version = "6.3.3"
+version_info = (6, 3, 3, 0)
 
 import importlib
 import typing