IONOS(simplenavigation): update submodule (theming migration changes, fix)

1.resize header icons

  References IONOS-Productivity/nc-simplenavigation#42 — mail/account
  icons 26px→30px, unified-search SVG max-size fix, icon gap 16px→8px.

2. fix parrword protected guest header

Signed-off-by: Tatjana Kaschperko Lindt <kaschperko-lindt@strato.de>

Author: tanyaka