Update git submodules

* Update helpcontent2 from branch 'master'
  - Don't set LANG env var by accident
    
    ...as setting a GNU Make LANG var exports it to recipes as an env var, and see
    e.g. 56bc0b1a "Don't set locale env vars on
    macOS" for potential problems caused by that.
    
    This is the help half of a change spanning the core and help repos.
    
    Change-Id: Ib5faf612e9030db384f7408ecd4fd03e65120f17
    Reviewed-on: https://gerrit.libreoffice.org/70930
    Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
    

helpcontent2 @ 8a21dc1c

-Subproject commit a1e2a03853bb6efebfc0e09679fef829d87745a9
+Subproject commit 8a21dc1cc51f0363b33e59b5c34c74d5c6737f1e