typescript-fetch: fix isCollectionFormatMulti for arrays of files (#8376)

Author: m1k1o

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/TypeScriptFetchClientCodegen.java

@@ -219,6 +219,14 @@ public Map<String, Object> postProcessModels(Map<String, Object> objs) {
         return objs;
     }
 
+    @Override
+    public void postProcessParameter(CodegenParameter parameter) {
+        super.postProcessParameter(parameter);
+        if (parameter.isFormParam && parameter.isArray && "binary".equals(parameter.dataFormat)) {
+            parameter.isCollectionFormatMulti = true;
+        }
+    }
+
     @Override
     public Map<String, Object> postProcessAllModels(Map<String, Object> objs) {
         Map<String, Object> result = super.postProcessAllModels(objs);