coverage: Use `-Copt-level=2` by default in run-coverage tests

This is a step towards being able to unify the two coverage test directories.

There are two tests that require adjustment:

- `overflow.rs` requires an explicit `-Coverflow-checks=yes`
- `sort_groups.rs` is sensitive to provably unused instantiations

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/run-coverage/sort_groups.coverage b/tests/run-coverage/sort_groups.coverage
index 8733bf48a9c..c70d7b3b282 100644
--- a/tests/run-coverage/sort_groups.coverage
+++ b/tests/run-coverage/sort_groups.coverage
@@ -7,7 +7,7 @@
    LL|      1|    let cond = std::env::args().len() > 1;
    LL|      1|    generic_fn::<()>(cond);
    LL|      1|    generic_fn::<&'static str>(!cond);
-   LL|      1|    if false {
+   LL|      1|    if std::hint::black_box(false) {
    LL|      0|        generic_fn::<char>(cond);
    LL|      1|    }
    LL|      1|    generic_fn::<i32>(cond);