d/control: Require dh-exec 0.23~, for build-profile support

Strictly speaking we might only need 0.15, but I'm not going to test
versions older than the jessie backport.

debian/control

@@ -14,7 +14,7 @@ Build-Depends:
  ca-certificates,
  cpio,
  debhelper (>= 10~),
- dh-exec,
+ dh-exec (>= 0.23~),
  docbook-xml <!nodoc>,
  docbook-xsl <!nodoc>,
  e2fslibs-dev,