docs: Fix template matching in page.xsl

Our last default template had a match of "node()" which incidentally matched
everything, including text nodes.  Since this has the same priority according to
the XSLT spec, section 5.5:

  https://www.w3.org/TR/1999/REC-xslt-19991116#conflict

this is an error.  Also according to the same spec section, the XSLT processor
may signal the error or pick the last rule.

This was uncovered with libxslt 1.1.35 which contains the following commit:

  https://gitlab.gnome.org/GNOME/libxslt/-/commit/b0074eeca3c6b21b4da14fdf712b853900c51635

which makes the build fail with:

  runtime error: file ../docs/page.xsl line 223 element element
  xsl:element: The effective name '' is not a valid QName.

because our last rule also matches text nodes and we are trying to extract the
node name out of them.

To fix this we change the match to "*" which only matches elements and not all
the nodes, and to avoid any possible errors with different XSLT processors we
also bump the priority of the match="text()" rule a little higher, just in case
someone needs to use an XSLT processor that chooses signalling the error instead
of the optional recovery.

https://bugs.gentoo.org/833586

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

docs/page.xsl

@@ -215,11 +215,11 @@
     </xsl:element>
   </xsl:template>
 
-  <xsl:template match="text()" mode="copy">
+  <xsl:template match="text()" mode="copy" priority="0">
     <xsl:value-of select="."/>
   </xsl:template>
 
-  <xsl:template match="node()" mode="copy">
+  <xsl:template match="*" mode="copy">
     <xsl:element name="{name()}">
       <xsl:copy-of select="./@*"/>
       <xsl:apply-templates mode="copy" />