Fix template conflict in XSLT with lxml>=4.9.0 again

Earlier attempt was fixing conflict with -1.0 priority attribute,
as a side effect of such low priority, SFC Actions were not
editable anymore.

This time move template around instead of using explicit priority.

                  <xsd:element name="OSX">
                    <xsd:complexType>
                      %(toolchain_gcc)s
                    </xsd:complexType>
                  </xsd:element>