ci: Move cargo test into ci/msrv.sh

We need `cargo` in our `PATH` and we already do the `PATH=...` dance in
`ci/msrv.sh`. This only worked before because we were inadvertedly
re-installing cargo when calling `ci/build.sh`, which was fixed in the
previous commit.

.cci.jenkinsfile

@@ -51,7 +51,6 @@ rust: {
       sh """
         set -xeuo pipefail
         ci/msrv.sh
-        cd rust && cargo test
       """
   }
 }}

ci/msrv.sh

@@ -7,7 +7,12 @@ MINIMUM_SUPPORTED_RUST_VERSION=1.39.0
 ci/installdeps.sh
 dnf remove -y cargo
 curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain ${MINIMUM_SUPPORTED_RUST_VERSION} -y
-PATH="$HOME/.cargo/bin:$PATH" SKIP_INSTALLDEPS=1 ci/build.sh |& tee out.txt
+export PATH="$HOME/.cargo/bin:$PATH"
+SKIP_INSTALLDEPS=1 ci/build.sh |& tee out.txt
 grep ${MINIMUM_SUPPORTED_RUST_VERSION} out.txt
 grep "checking for cargo... $HOME/.cargo/bin/cargo" out.txt
 grep "checking for rustc... $HOME/.cargo/bin/rustc" out.txt
+
+# and run the tests
+cd rust
+cargo test