debian: Bump compat to 12

This makes some things simpler like dh_nissing and it moves
phosh to /u/libexec where it should have always been.
Signed-off-by: Guido Günther <guido.gunther@puri.sm>

debian/compat

-11
+12

debian/control

@@ -3,7 +3,7 @@ Section: x11
 Priority: optional
 Maintainer: Guido Günther <agx@sigxcpu.org>
 Build-Depends:
- debhelper (>= 10),
+ debhelper (>= 12),
  libgcr-3-dev,
  libgnome-desktop-3-dev,
  libgtk-3-dev,