C#/Java: Add test for missing neutral summary generation.

java/ql/test/utils/modelgenerator/dataflow/CaptureNeutralModels.ext.yml

@@ -0,0 +1,7 @@
+extensions:
+  - addsTo:
+      pack: codeql/java-all
+      extensible: neutralModel
+    data:
+      - [ "p", "Sinks", "nosink", "(Object)", "sink", "manual"]
+      - [ "p", "Sinks", "nosink", "(Object)", "summary", "df-generated"]

java/ql/test/utils/modelgenerator/dataflow/p/Sinks.java

@@ -21,6 +21,11 @@ public class Sinks {
   // neutral=p;Sinks;sink2;(Object);summary;df-generated
   public void sink2(Object o) {}
 
+  // Defined as sink neutral file in the model file next to the
+  // neutral test.
+  // MISSING NEUTRAL.
+  public void nosink(Object o) {}
+
   // sink=p;Sinks;true;copyFileToDirectory;(Path,Path,CopyOption[]);;Argument[0];path-injection;df-generated
   // sink=p;Sinks;true;copyFileToDirectory;(Path,Path,CopyOption[]);;Argument[1];path-injection;df-generated
   // neutral=p;Sinks;copyFileToDirectory;(Path,Path,CopyOption[]);summary;df-generated