component/slapos: fix for riscv architecture

This is a fixup of 210e2d76.

component/slapos/obs.cfg

@@ -100,7 +100,7 @@ environment +=
   PERL5LIB=${perl:location}/lib/5.38.0/
 
 [gobject-introspection]
-pre-configure =
+pre-configure +=
   sed -i 's#!/opt/slapos/parts/python${python:version}/bin/python${python:version}#!${python:location}/bin/python${python:version}#' ${python:location}/bin/python${python:version}-config
 configure-options +=
   --enable-shared