Preserve unused locals in some stable-mir tests

Author: scottmcm

Diff for: tests/ui-fulldeps/stable-mir/check_allocation.rs

@@ -224,6 +224,7 @@ fn main() {
     let args = vec![
         "rustc".to_string(),
         "--edition=2021".to_string(),
+        "-Cdebuginfo=full".to_string(),
         "--crate-name".to_string(),
         CRATE_NAME.to_string(),
         path.to_string(),

Diff for: tests/ui-fulldeps/stable-mir/check_ty_fold.rs

@@ -81,6 +81,7 @@ fn main() {
     let args = vec![
         "rustc".to_string(),
         "-Cpanic=abort".to_string(),
+        "-Cdebuginfo=full".to_string(),
         "--crate-name".to_string(),
         CRATE_NAME.to_string(),
         path.to_string(),