Fixes build error 'Versioning for this project requires either an sdist tarball, or access to an upstream git repository'
--- psi4-1.8.1/external/downstream/snsmp2/CMakeLists.txt       2023-02-22 14:56:49.000000000 +0000
+++ psi4-1.8.1/external/downstream/snsmp2/CMakeLists.txt      2023-02-22 15:00:11.000000000 +0000
@@ -22,7 +22,7 @@
             URL https://github.com/DEShawResearch/sns-mp2/archive/12462c6.tar.gz  # v1.0 + 26
             CONFIGURE_COMMAND ""
             UPDATE_COMMAND ""
-            BUILD_COMMAND ${Python_EXECUTABLE} setup.py build
+            BUILD_COMMAND PBR_VERSION=1.0 ${Python_EXECUTABLE} setup.py build
             BUILD_IN_SOURCE 1
-            INSTALL_COMMAND ${Python_EXECUTABLE} setup.py install
+            INSTALL_COMMAND PBR_VERSION=1.0 ${Python_EXECUTABLE} setup.py install
                                                           --record=record.txt
                                                           --single-version-externally-managed
                                                           --install-lib=${STAGED_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}${PYMOD_INSTALL_LIBDIR})