m4/sage_python_package_check.m4: Use 'export PYTHONUSERBASE'

Author: Matthias Koeppe

m4/sage_python_package_check.m4

@@ -76,7 +76,7 @@ AC_DEFUN([SAGE_PYTHON_PACKAGE_CHECK], [
         dnl dependencies like python_version<'3.11' will have single
         dnl quotes in them. (We normalized the quotes earlier with sed.)
         AS_IF(
-          [PYTHONUSERBASE="${PYTHONUSERBASE}" config.venv/bin/python3 -c   dnl
+          [config.venv/bin/python3 -c   dnl
              "import pkg_resources;                                        dnl
               pkg_resources.require(\"${SAGE_PKG_VERSPEC}\".splitlines())" dnl
            2>&AS_MESSAGE_LOG_FD],
@@ -129,6 +129,7 @@ AC_DEFUN([WITH_SAGE_PYTHONUSERBASE], [dnl
   PYTHONUSERBASE_SAVED="${PYTHONUSERBASE}"
   AS_IF([test -z "${PYTHONUSERBASE}"], [
     PYTHONUSERBASE="${HOME}/.sage/local"
+    export PYTHONUSERBASE
   ])
   $1
   PYTHONUSERBASE="${PYTHONUSERBASE_SAVED}"