test(qwen3-tts-cpp): ignore the warmup error in the blocking spec

The spec only checks that warmupBatch returns once every request ends;
errcheck flags the dropped error value.

Assisted-by: Claude:claude-sonnet-5-5 golangci-lint
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/go/qwen3-tts-cpp/qwen3ttscpp_test.go

@@ -289,7 +289,7 @@ var _ = Describe("batch warmup", func() {
 			return 0
 		}
 		done := make(chan struct{})
-		go func() { warmupBatch(3); close(done) }()
+		go func() { _ = warmupBatch(3); close(done) }()
 		Eventually(done).WithTimeout(5 * time.Second).Should(BeClosed())
 		Expect(texts).To(ConsistOf("Hello there.", "Hello there. Hello there.", "Hello there. Hello there. Hello there."))
 	})