Switch instrument coverage to stable

.github/workflows/cron-ci.yaml

@@ -15,10 +15,6 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: nightly
-          override: true
-          components: llvm-tools-preview
       - run: sudo apt-get update && sudo apt-get -y install lcov
       - uses: actions-rs/cargo@v1
         with:

scripts/codecoverage-rustc-wrapper.sh

@@ -14,7 +14,7 @@ get_crate_name() {
 
 case $(get_crate_name "$@") in
   rustpython_*|rustpython)
-    EXTRA=(-Zinstrument-coverage)
+    EXTRA=(-Cinstrument-coverage)
     ;;
 
   *) EXTRA=() ;;