docs/migrating.adoc: document the tarball suffix update for Cargo-fetch packages

We changed the suffix of tarballs for Cargo-fetched packages, which
affects out-of-tree packages, so it makes sense to document that in
the migration guide.

Reported-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>

docs/manual/migrating.adoc

@@ -209,3 +209,9 @@ or with a startup script.
 Note that systems using systemd are not impacted: systemd always ensures
 that `/run` is writable. Systems further using systemd-resolved already
 had a `/etc/resolv.conf` that pointed into `/run` anyway.
+
+Due to the update of Rust to a version greater than 1.84.0 making the
+Cargo.lock file mandatory and the change from +.cargo/config+ to
++.cargo/config.toml+, tarballs generated by Cargo-fetched packages
+have changed. Therefore the suffix of such tarballs has been changed
+from +-cargo2+ to +-cargo4+.