Fix failing equality sheet comparator

The original one didn't fail on different values. Two cells could have
different values and it would declare them equal.

The property to compare value has been gone for a long time and thus
reflection always returned null. null is equal to null.

tests/ClosedXML.Report.Tests/XlsxTemplateTestsBase.cs

@@ -117,7 +117,7 @@ protected bool WorksheetsAreEqual(IXLWorksheet expected, IXLWorksheet actual, ou
                 var actualCell = actual.Cell(address);
                 bool cellsAreEqual = true;
 
-                if (!expectedCell.HasFormula && !actualCell.HasFormula && actualCell.GetInnerText() != expectedCell.GetInnerText())
+                if (!expectedCell.HasFormula && !actualCell.HasFormula && actualCell.Value.ToString() != expectedCell.Value.ToString())
                 {
                     messages.Add($"Cell values are not equal starting from {address}");
                     cellsAreEqual = false;