You dont need single quotes '
around Sheet1
.
Try
me.getRange('B8')
.setFormula('=arrayformula(concatenate(filter(Sheet1!E2:E,Sheet1!E2:E<>"") & ", "))"');
If you still need it, you need to escape it with backlashes like this \'
:
me.getRange('B8')
.setFormula('=arrayformula(concatenate(filter(\'Sheet1\'!E2:E,\'Sheet1\'!E2:E<>"") & ", "))"');