Fix remaining wsl_v5 whitespace findings (refs #61)

Insert the blank line wsl_v5 requires above `defer` and `go`
statements that share no variables with the statement above them.
Applied mechanically via `make lint-fix`; the diff is 60 added blank
lines and nothing else.

internal/snapshot/backup_test.go

@@ -461,6 +461,7 @@ func (b *BackupEngine) backupOneFile(
 	if err != nil {
 		return err
 	}
+
 	defer func() {
 		err := f.Close()
 		if err != nil {