OSO backfill: memcached log formatting error

Build: 7.2.1-5799

Steps:

• 2 node KV + 1 node n1ql:index cluster with vbuckets=2
• Create Magma bucket with 3 custom collections (c1,c2,c3) and load 300K items on each of them
• Create GSI index on collection 'c1'

Seeing the following error in memcached.log

2023-06-26T03:30:25.240229-07:00 ERROR BucketLogger::logInner: Failed to log message with format string '{} Skipping OSO backfill for cid:{} as collection item count ({}) is too large a percentage of the vBucket item count ({:.2f}%)

Note: Found this while testing MB-57106