clean up supporting-mustache (#18524)

Author: wing328

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

@@ -910,7 +910,7 @@ public void postProcessFile(File file, String fileType) {
         // only process the following type (or we can simply rely on the file extension to check if it's a .c or .h file)
         Set<String> supportedFileType = new HashSet<>(
                 Arrays.asList(
-                        "supporting-mustache",
+                        "supporting-file",
                         "model-test",
                         "model",
                         "api-test",