Fix comment in regression tests for large objects
The values assigned to INV_WRITE and INV_READ were reversed in the
tests, which would be confusing when writing tests specific to read or
write operations on LOs.
Author: Yugo Nagata
Discussion: https://postgr.es/m/
20220527153028.
61a4608f66abcd026fd3806f@sraoss.co.jp