sw btlr writing mode: add odf spec proposal URL

Change-Id: I7848677cf4c8246fc7a1833bec809945fb541b29
Reviewed-on: https://gerrit.libreoffice.org/67814
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
diff --git a/schema/libreoffice/OpenDocument-schema-v1.3+libreoffice.rng b/schema/libreoffice/OpenDocument-schema-v1.3+libreoffice.rng
index 956ccc2..19786f8 100644
--- a/schema/libreoffice/OpenDocument-schema-v1.3+libreoffice.rng
+++ b/schema/libreoffice/OpenDocument-schema-v1.3+libreoffice.rng
@@ -2323,7 +2323,7 @@ xmlns:loext="urn:org:documentfoundation:names:experimental:office:xmlns:loext:1.
    </rng:optional>
  </rng:define>

  <!-- TODO no proposal -->
  <!-- https://issues.oasis-open.org/browse/OFFICE-4030 -->
  <rng:define name="common-writing-mode-attlist" combine="interleave">
    <rng:optional>
      <rng:attribute name="loext:writing-mode">