Update C++/CMake policy based on Ubuntu 22.04 (#3666)

Author: paulromano

docs/source/devguide/policies.rst

@@ -21,8 +21,8 @@ C++ code in OpenMC must conform to the most recent C++ standard that is fully
 supported in the `version of the gcc compiler
 <https://gcc.gnu.org/projects/cxx-status.html>`_ that is distributed with the
 oldest version of Ubuntu that is still within its `standard support period
-<https://ubuntu.com/about/release-cycle>`_. Ubuntu 20.04 LTS will be supported
-through April 2025 and is distributed with gcc 9.3.0, which fully supports the
+<https://ubuntu.com/about/release-cycle>`_. Ubuntu 22.04 LTS will be supported
+through April 2027 and is distributed with gcc 11.4.0, which fully supports the
 C++17 standard.
 
 --------------------
@@ -31,5 +31,5 @@ CMake Version Policy
 
 Similar to the C++ standard policy, the minimum supported version of CMake
 corresponds to whatever version is distributed with the oldest version of Ubuntu
-still within its standard support period. Ubuntu 20.04 LTS is distributed with
-CMake 3.16.
+still within its standard support period. Ubuntu 22.04 LTS is distributed with
+CMake 3.22.