MissionItemTest: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

src/MissionManager/MissionItemTest.cc

@@ -237,7 +237,7 @@ void MissionItemTest::_testFactSignals(void)
     QCOMPARE(arguments.at(0).toDouble(), 8.0);
 }
 
-void MissionItemTest::_checkExpectedMissionItem(const MissionItem& missionItem, bool allNaNs)
+void MissionItemTest::_checkExpectedMissionItem(const MissionItem& missionItem, bool allNaNs) const
 {
     QCOMPARE(missionItem.sequenceNumber(), _seq);
     QCOMPARE(missionItem.isCurrentItem(), false);

src/MissionManager/MissionItemTest.h

@@ -40,7 +40,7 @@ private slots:
     void _testSaveToJson(void);
 
 private:
-    void _checkExpectedMissionItem(const MissionItem& missionItem, bool allNaNs = false);
+    void _checkExpectedMissionItem(const MissionItem& missionItem, bool allNaNs = false) const;
     QJsonObject _createV1Json(void);
     QJsonObject _createV2Json(void);
     QJsonObject _createV3Json(bool allNaNs = false);