Ports: Add missing version.sh file to python3 port

I thought I had committed this, but it's .gitignore'd. Add an exception
to Ports/.gitignore and add it for real this time. :^)

Fixes #5008.

Ports/.gitignore

@@ -4,3 +4,4 @@
 !*/patches/*
 !*/.gitignore
 !*/README.md
+!python3/version.sh

Ports/python3/version.sh

@@ -0,0 +1,4 @@
+PYTHON_VERSION="3.9.1"
+PYTHON_ARCHIVE="Python-${PYTHON_VERSION}.tar.xz"
+PYTHON_ARCHIVE_URL="https://www.python.org/ftp/python/${PYTHON_VERSION}/${PYTHON_ARCHIVE}"
+PYTHON_ARCHIVE_MD5SUM="61981498e75ac8f00adcb908281fadb6"