Fixes test by providing correct end date for expected result

Author: kevwhitt-hee

DigitalLearningSolutions.Web.Tests/Services/ActivityServiceTests.cs

@@ -436,7 +436,7 @@ public void GetActivityDataFileForCentre_returns_expected_excel_data()
 
             var filterData = new ActivityFilterData(
                 DateTime.Parse("2020-9-1"),
-                DateTime.Parse("2021-9-1"),
+                DateTime.Parse("2021-9-30"),
                 null,
                 null,
                 null,