Fix breaking change to rustup (#389)

Author: bnaecker

.github/buildomat/jobs/build-and-test.sh

@@ -11,6 +11,7 @@ set -o errexit
 set -o pipefail
 set -o xtrace
 
+rustup show active-toolchain || rustup toolchain install
 cargo --version
 rustc --version
 

.github/buildomat/jobs/test-no-op-implementation.sh

@@ -11,6 +11,7 @@ set -o errexit
 set -o pipefail
 set -o xtrace
 
+rustup show active-toolchain || rustup toolchain install
 cargo --version
 rustc --version