eth: fix typo in comment (#25327)

eth/api.go

@@ -157,7 +157,7 @@ func (api *AdminAPI) ExportChain(file string, first *uint64, last *uint64) (bool
 	}
 	if _, err := os.Stat(file); err == nil {
 		// File already exists. Allowing overwrite could be a DoS vector,
-		// since the 'file' may point to arbitrary paths on the drive
+		// since the 'file' may point to arbitrary paths on the drive.
 		return false, errors.New("location would overwrite an existing file")
 	}
 	// Make sure we can create the file to export into