configure.ac: disable soupsieve with --disable-notebook

The soupsieve package is a dependency of beautifulsoup4, which is
already disabled with --disable-notebook. It should therefore be safe
to disable soupsieve under the same circumstances.

Author: orlitzky

configure.ac

@@ -507,7 +507,7 @@ AC_ARG_ENABLE([cvxopt],
 AC_ARG_ENABLE([notebook],
   AS_HELP_STRING([--disable-notebook],
                  [disable build of the Jupyter notebook and related packages]), [
-    for pkg in notebook nbconvert beautifulsoup4 sagenb_export nbformat nbclient terminado send2trash prometheus_client mistune pandocfilters bleach defusedxml jsonschema jupyter_jsmol argon2_cffi argon2_cffi_bindings webencodings tinycss2; do
+    for pkg in notebook nbconvert beautifulsoup4 sagenb_export nbformat nbclient terminado send2trash prometheus_client mistune pandocfilters bleach defusedxml jsonschema jupyter_jsmol argon2_cffi argon2_cffi_bindings webencodings tinycss2 soupsieve; do
       AS_VAR_SET([SAGE_ENABLE_$pkg], [$enableval])
     done
   ])