Rust: Fix bad join

Author: hvitved

rust/ql/lib/codeql/rust/internal/TypeInference.qll

@@ -1044,6 +1044,9 @@ private Type inferTryExprType(TryExpr te, TypePath path) {
   )
 }
 
+pragma[nomagic]
+private StructType getStrStruct() { result = TStruct(any(Builtins::Str s)) }
+
 pragma[nomagic]
 private Type inferLiteralType(LiteralExpr le, TypePath path) {
   path.isEmpty() and
@@ -1074,7 +1077,7 @@ private Type inferLiteralType(LiteralExpr le, TypePath path) {
     path.isEmpty() and result = TRefType()
     or
     path = TypePath::singleton(TRefTypeParameter()) and
-    result = TStruct(any(Builtins::Str s))
+    result = getStrStruct()
   )
 }