Avoid linting for $$ with &convert

Attributes on a field with `&convert` make `$$` mean something
different. $$ refers to before the conversion, `self.field` revers to
after.

rule-tests/use-dd-test.yml

@@ -3,6 +3,7 @@ valid:
   - "type X = unit { x: uint8 { $$; } };"
   - "type X = unit { x: uint8 { other.y; } };"
   - "type X = unit { y: uint8 { self.x; } };"
+  - "type X = unit { x: uint8 &convert=$$ + 5 { self.x; $$; } };"
 invalid:
   - "type X = unit { x: uint8 { self.x; } };"
   - "type X = unit { x: uint8 { if (True) self.x; } };"

rules/use-dd.yml

@@ -25,6 +25,13 @@ rule:
               field: "name"
               kind: "ident"
               pattern: "$F"
+        not:
+          inside:
+            kind: "field_decl"
+            stopBy: "end"
+            has:
+              kind: "attribute"
+              regex: "&convert"
 
 fix: "$$"