fix: update clickbench.slt to reflect Inexact NDV physical plan

NDV from parquet statistics is always Inexact, so the AggregateStatistics
optimizer cannot fold COUNT(DISTINCT) to a constant. Update the EXPLAIN
plan to match the actual AggregateExec output.

Author: Rich-T-kid

datafusion/sqllogictest/test_files/clickbench.slt

@@ -1203,8 +1203,8 @@ logical_plan
 02)--SubqueryAlias: hits
 03)----TableScan: hits_raw projection=[HitColor, BrowserLanguage, BrowserCountry]
 physical_plan
-01)ProjectionExec: expr=[1 as count(DISTINCT hits.HitColor), 1 as count(DISTINCT hits.BrowserCountry), 1 as count(DISTINCT hits.BrowserLanguage)]
-02)--PlaceholderRowExec
+01)AggregateExec: mode=Single, gby=[], aggr=[count(DISTINCT hits.HitColor), count(DISTINCT hits.BrowserCountry), count(DISTINCT hits.BrowserLanguage)]
+02)--DataSourceExec: file_groups={1 group: [[WORKSPACE_ROOT/datafusion/core/tests/data/clickbench_hits_10.parquet]]}, projection=[HitColor, BrowserLanguage, BrowserCountry], file_type=parquet
 
 query III
 SELECT COUNT(DISTINCT "HitColor"), COUNT(DISTINCT "BrowserCountry"), COUNT(DISTINCT "BrowserLanguage")  FROM hits;