Update git submodules

* Update helpcontent2 from branch 'master'
  - Propagate xsltproc failure, part 2
    
    ...following up on c3509fb7e6675a38560c7e2764b21861d1e23362 "Propagate xsltproc
    failure".  The while loops would only have a non-zero exit code if the xsltproc
    invocation in the last iteration of the loop fails.  (Oddly, adding `set -e`
    instead seems to have no effect.)
    
    Change-Id: I9296a59147697595ebe7b0d2b742044f8a8a3f02
    Reviewed-on: https://gerrit.libreoffice.org/68309
    Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
    

helpcontent2 @ a72b5e90

-Subproject commit b2bd7773ca2b07667d9ce379fac9327c52539d18
+Subproject commit a72b5e90798aedb8945da175534986791d3d3352