.github: Add app-text/docbook-xsl-ns-stylesheets to automation

Signed-off-by: Krzesimir Nowak <knowak@microsoft.com>

Author: krnowak

.github/workflows/portage-stable-packages-list

@@ -179,6 +179,7 @@ app-shells/gentoo-bashcomp
 app-text/asciidoc
 app-text/build-docbook-catalog
 app-text/docbook-xml-dtd
+app-text/docbook-xsl-ns-stylesheets
 app-text/docbook-xsl-stylesheets
 app-text/mandoc
 app-text/manpager