Install and use nightly-2022-01-14

We are pinning it to a version where coverage works.
Ref: rust-lang/rust#93054

Author: lpenz

Dockerfile

@@ -4,6 +4,8 @@
 
 FROM rust:slim
 RUN set -e -x; \
+    rustup toolchain install nightly-2022-01-14; \
+    rustup default nightly-2022-01-14; \
     rustup component add llvm-tools-preview; \
     cargo install cargo-llvm-cov