ci: fix miri checks (#1651)

Fixes #1650

Manual run:
https://github.com/CQCL/hugr/actions/runs/11815871369/job/32917969928

hugr-model/tests/text.rs

@@ -13,6 +13,7 @@ pub fn test_declarative_extensions() {
 }
 
 #[test]
+#[cfg_attr(miri, ignore)] // Opening files is not supported in (isolated) miri
 pub fn test_literals() {
     insta::assert_snapshot!(roundtrip(include_str!("fixtures/model-literals.edn")))
 }