Add MaD barrier guard model to make test pass

Author: owen-mc

rust/ql/test/library-tests/dataflow/barrier/inline-flow.ext.yml

@@ -4,3 +4,8 @@ extensions:
       extensible: barrierModel
     data:
       - ["main::sanitize", "ReturnValue", "test-barrier", "manual"]
+  - addsTo:
+      pack: codeql/rust-all
+      extensible: barrierGuardModel
+    data:
+      - ["main::verify_safe", "Argument[0]", "true", "test-barrier", "manual"]

rust/ql/test/library-tests/dataflow/barrier/main.rs

@@ -43,6 +43,6 @@ fn verify_safe(s: &str) -> bool {
 fn with_barrier_guard() {
     let s = source(1);
     if verify_safe(s) {
-        sink(s); // $ SPURIOUS: hasValueFlow=1
+        sink(s);
     }
 }