sql: fix flaky TestIndexSplitAndScatterWithStats

The test was flaky because the stats cache could contain a stale entry
(populated during INSERT planning) when MaybeSplitIndexSpans ran during
CREATE INDEX. Despite its name, GetFreshTableStats returns cached data
without checking whether stats have been updated. The async cache
refresh triggered by CREATE STATISTICS may not complete in time.

Fix by invalidating the stats cache on all nodes after CREATE STATISTICS,
forcing a fresh read from the database.

Fixes: #170609

Release note: None

Co-Authored-By: roachdev-claude <roachdev-claude-bot@cockroachlabs.com>

Author: michae2

pkg/sql/index_split_scatter_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/config"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/sql"
+	"github.com/cockroachdb/cockroach/pkg/sql/catalog/descpb"
 	"github.com/cockroachdb/cockroach/pkg/testutils"
 	"github.com/cockroachdb/cockroach/pkg/testutils/serverutils"
 	"github.com/cockroachdb/cockroach/pkg/testutils/skip"
@@ -165,6 +166,12 @@ func TestIndexSplitAndScatterWithStats(t *testing.T) {
 		// Generate statistics for these tables.
 		if statsExist {
 			runner.Exec(t, "CREATE STATISTICS st FROM multi_column_split")
+			// Force a stats cache refresh on all nodes so
+			// MaybeSplitIndexSpans sees the new stats.
+			tableID := descpb.ID(sqlutils.QueryTableID(t, cluster.ServerConn(0), "defaultdb", "public", "multi_column_split"))
+			for i := 0; i < numNodes; i++ {
+				cluster.Server(i).ExecutorConfig().(sql.ExecutorConfig).TableStatsCache.InvalidateTableStats(ctx, tableID)
+			}
 		}
 		// Next create indexes on both tables.
 		splitHookEnabled.Store(true)