C#: Avoid generating new source models on 'file' kind sources.

java/ql/src/utils/model-generator/internal/CaptureModels.qll

@@ -234,6 +234,7 @@ string captureSource(TargetApi api) {
     config.hasFlow(source, sink) and
     ExternalFlow::sourceNode(source, kind) and
     api = sink.getEnclosingCallable() and
+    isRelevantSourceKind(kind) and
     result = asSourceModel(api, returnNodeAsOutput(sink), kind)
   )
 }

java/ql/src/utils/model-generator/internal/CaptureModelsSpecific.qll

@@ -259,3 +259,9 @@ predicate isRelevantSinkKind(string kind) {
   not kind.matches("regex-use%") and
   not kind = "write-file"
 }
+
+/**
+ * Holds if `kind` is a relevant source kind for creating source models.
+ */
+bindingset[kind]
+predicate isRelevantSourceKind(string kind) { any() }