[chore][receiver/purefb] Enable goleak check

[crobert-1]

Description:

This change enables goleak checks on the Pure Storage FlashBlade receiver to help ensure no goroutines are being leaked. This is a test only change as a test was missing a shutdown call.

This looks like I deleted a test, but the two tests were identical, other than a missing shutdown call. Once the missing call was added they were identical, so I decided to delete one. I also consolidated err checking to remove the err variable and directly check the result of the Start and Shutdown methods.

Link to tracking Issue:
#30438

Testing:
All existing tests are passing, as well as added goleak check.