Avoid issues caused by having a workbook with the same name opened in Excel during PSBlitz execution

[VladDBA]

There are cases when a user might want to run PSBlitz at the same while their looking at a previously generated output for the same instance. Due to the Excel output file using the PSBlitzOutput_[Instance][_DatabaseName].xlsx naming format, which isn't very unique, there are chances that this might lead to the "Sorry, Excel can’t open two workbooks with the same name" error.