debian: Add deb-conffiles(5) to dpkg-dev package

Missed in commit 90e33b3495cb60c2008673aedf467a796ff85a41.

debian/dpkg-dev.manpages

@@ -1,6 +1,7 @@
 debian/tmp/usr/share/man/*/deb-changelog.5
 debian/tmp/usr/share/man/*/deb-changes.5
 debian/tmp/usr/share/man/*/deb-control.5
+debian/tmp/usr/share/man/*/deb-conffiles.5
 debian/tmp/usr/share/man/*/deb-src-control.5
 debian/tmp/usr/share/man/*/deb-version.5
 debian/tmp/usr/share/man/*/deb-substvars.5