Fix test for import-backend

Another split function needed mocking

libgnucash/engine/mocks/gmock-Split.cpp

@@ -103,6 +103,13 @@ xaccSplitGetMemo (const Split *split)
     return mocksplit ? mocksplit->get_memo() : "";
 }
 
+void
+xaccSplitSetMemo (Split *split, const char *memo)
+{
+    ASSERT_TRUE(GNC_IS_MOCKSPLIT(split));
+    gnc_mocksplit(split)->set_memo(memo);
+}
+
 char
 xaccSplitGetReconcile (const Split *split)
 {

libgnucash/engine/mocks/gmock-Split.h

@@ -71,6 +71,7 @@ public:
     MOCK_CONST_METHOD0(get_value, gnc_numeric());
     MOCK_METHOD1(set_value, void(gnc_numeric));
     MOCK_CONST_METHOD0(get_memo, const char *());
+    MOCK_METHOD1(set_memo, void(const char *));
     MOCK_CONST_METHOD0(get_reconcile, char());
     MOCK_METHOD1(set_reconcile, void(char));
     MOCK_METHOD1(set_date_reconciled_secs, void(time64));