Run miri in stricter miri-strict-provenance mode

Author: dtolnay

.github/workflows/ci.yml

@@ -86,7 +86,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@miri
       - run: cargo miri test
         env:
-          MIRIFLAGS: -Zmiri-tag-raw-pointers
+          MIRIFLAGS: -Zmiri-strict-provenance
 
   outdated:
     name: Outdated