Fix search near returning wrong key/value sometimes when key doesn't exist

As part of implementing WT-8707, a bug was uncovered in develop. Note: checkpoint test was slightly modified to reproduce this bug.

Test command: 

./test_checkpoint -t r -W 1 -r 1 -s 1 -x -n 100000 -k 100000 -C cache_size=10MB 

The bug scenario is described below:

• Keys in btree (sorted order)
  •  key: 52454
    • value: 9704
    • commit timestamp: 904
  • key:52471 
    • value: 1289
    • commit timestamp: 22

• Performed a search near (read timestamp: 795)
  • Key Searched: 52459 (doesn't exist in btree)
  • Value returned 1289
  • However, the key returned was 52454.

Note: Even though the test fails consistently, the scenario described above fails rarely, mostly the correct key is returned.