Install latest llvm for code coverage

.github/workflows/actions.yml

@@ -94,7 +94,7 @@ jobs:
         run: |
           RUSTFLAGS="-C instrument-coverage" \
             cargo test --workspace -- --quiet
-          sudo apt-get install -yq llvm
+          sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)"
           llvm-profdata merge -sparse */*.profraw -o fend.profdata
           llvm-cov report \
             --use-color \