tst_bench_QCryptographicHash: swallow result() return values

As usual, assign them to a [[maybe_unused]] variable, to avoid
potential future [[nodiscard]] problems, and to indicate to
readers of the code that there's a result that's being returned,
we're just not interested in it.

Pick-to: 6.5 6.2
Change-Id: I2bd47ca98418092ca885d50a1a6417a21a612a85
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

tests/benchmarks/corelib/tools/qcryptographichash/tst_bench_qcryptographichash.cpp

@@ -82,7 +82,8 @@ void tst_QCryptographicHash::hash()
     QFETCH(QByteArray, data);
 
     QBENCHMARK {
-        QCryptographicHash::hash(data, algo);
+        [[maybe_unused]]
+        auto r = QCryptographicHash::hash(data, algo);
     }
 }
 
@@ -95,7 +96,8 @@ void tst_QCryptographicHash::addData()
     QBENCHMARK {
         hash.reset();
         hash.addData(data);
-        hash.result();
+        [[maybe_unused]]
+        auto r = hash.result();
     }
 }
 
@@ -113,7 +115,8 @@ void tst_QCryptographicHash::addDataChunked()
             hash.addData({data.constData() + 64 * i, 64});
         hash.addData({data.constData() + data.size() / 64 * 64, data.size() % 64});
 
-        hash.result();
+        [[maybe_unused]]
+        auto r = hash.result();
     }
 }