* fix: typo incrementing instead of decrementing
* Add tests for MostSeen decrement bug
This bug requires a specific set of circumstances to trigger
and become visible:
1. decrement a label that is non-zero but not first
2. repeat the decrement at least best_count()/2 times
3. increment that label
4. check the best count
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Co-authored-by: teor <teor@riseup.net>
