Regression of WT-18117 (test_size_stats01 'scanned' != 'key_count').

Failure (recovered from task log; BuildBaron extracted no fault):

FAIL: test_size_stats01.test_size_stats01.test_size_metrics
  File ".../test/suite/test_size_stats01.py", line 169, in test_size_metrics
    self.assertEqual(s['scanned'], s['key_count'])
AssertionError: 1000 != 3106

Why this is a regression, not a duplicate of WT-18117:
WT-18117 was Closed/Fixed by PR #14232 (develop commit a65412c9, merged 2026-07-17). This failure is on wiredtiger commit 6fb83cc4 (2026-07-20 03:35 UTC). git merge-base --is-ancestor a65412c9 6fb83cc4 returns true, i.e. the WT-18117 fix is already present in this failing tree, yet the same assertion fails again. The original fix is therefore incomplete or the assertion remains flaky. WT-18117 is GA Released (16/07/2026), so a follow-up BF is filed instead of reopening.

• unit-test-bucket09 on amazon2023-arm64-asan
• Host: i-07a59a525e91ff572
• Commit: 6fb83cc4
• task log