chore: Fix miri test (#1938)

Fixes #1931 

Test run: https://github.com/CQCL/hugr/actions/runs/13549274743

drive-by: Fix automated issue comment, and check target branch before
making the comments

Semver-checks failing due to #1940

.github/workflows/unsoundness.yml

@@ -41,14 +41,14 @@ jobs:
   create-issue:
     uses: CQCL/hugrverse-actions/.github/workflows/create-issue.yml@main
     needs: miri
-    if: always() && needs.miri.result == 'failure'
+    if: always() && needs.miri.result == 'failure' && github.ref == 'refs/heads/main'
     secrets:
         GITHUB_PAT: ${{ secrets.HUGRBOT_PAT }}
     with:
-        title: "💥 Unsoundness check failed on main"
+        title: "💥 Unsoundness check fail on main"
         body: |
             The unsoundness check for `CQCL/hugr` failed.
 
-            [https://github.com/CQCL/hugr/actions/runs/${{ github.run_id }}](Please investigate).
+            [Please investigate](https://github.com/CQCL/hugr/actions/runs/${{ github.run_id }}).
         unique-label: "unsoundness-checks"
         other-labels: "bug"

hugr-core/src/ops/constant.rs

@@ -817,6 +817,9 @@ pub(crate) mod test {
     #[case(const_tuple_serialized(), const_tuple())]
     #[case(const_array_bool(), const_array_bool())]
     #[case(const_array_options(), const_array_options())]
+    // Opaque constants don't get resolved into concrete types when running miri,
+    // as the `typetag` machinery is not available.
+    #[cfg_attr(miri, ignore)]
     fn const_serde_roundtrip(#[case] const_value: Value, #[case] expected_value: Value) {
         let serialized = serde_json::to_string(&const_value).unwrap();
         let deserialized: Value = serde_json::from_str(&serialized).unwrap();