Fix build on supported platforms due to `log` breakage

Fix build on supported platforms due to `log` breakage

The `log` crate decided to break support for rustc 1.48 (Debian
bullseye) the day the next release of Debian comes out, obviously
before anyone has had a chance to upgrade to the new Debian
bookworm (at https://github.com/rust-lang/log/pull/543). Thus, we
have to manually pin it back to the previous release.

Sadly, the `log` crate is a transitive dependency of `tokio` until
0.20, which requires rustc 1.49. Luckily at least we won't have to
deal with this again, as `log` won't be a dependency of ours
anymore soon.