Adapt rustc_data_structures tests to run in strict miri

Some tests took too long and owning_ref is fundamentally flawed,
so don't run these tests or run them with a shorter N. This makes
miri with `-Zmiri-strict-provenance` usable to find UB.

compiler/rustc_data_structures/src/graph/scc/tests.rs

@@ -156,7 +156,10 @@ fn test_deep_linear() {
     v
     …
      */
+    #[cfg(not(miri))]
     const NR_NODES: usize = 1 << 14;
+    #[cfg(miri)]
+    const NR_NODES: usize = 1 << 3;
     let mut nodes = vec![];
     for i in 1..NR_NODES {
         nodes.push((i - 1, i));