Add cargo-web and rustc-web in Build-Conflicts

Depending how apt parse the build-deps list, it can fail to
resolve dependencies with:

The following packages have unmet dependencies:
 libstd-rust-web-dev : Conflicts: libstd-rust-dev
 rustc-web : Conflicts: rustc but 1.63.0+dfsg1-2+apertis1bv2025dev3b1 is to be installed

Actually, doing a "apt build-dep ." works, but it fails after
a "wrap-and-sort" like it is used in ci-buildpackage. That is because
the order between dh-cargo and cargo:native is inverted. So, to avoid
potential conflicts, makes sure we don't pull the "-web" variants
which are only used to build firefox.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

debian/control

@@ -44,6 +44,7 @@ Build-Depends: debhelper (>= 12),
  librust-procfs-dev, librust-terminal-size-dev (>= 0.2.1),
  librust-indicatif-dev (>= 0.17.3),
  librust-backtrace-sys-dev, python3-sphinx, help2man
+Build-Conflicts: cargo-web, rustc-web
 Maintainer: Debian Rust Maintainers <pkg-rust-maintainers@alioth-lists.debian.net>
 Uploaders:
  Sylvestre Ledru <sylvestre@debian.org>