roachtest: query only primary index in SHOW RANGES

The semantics of SHOW RANGES has changed in 5604fea, it now includes ranges of
the secondary indicies. This change fixes the query to only request ranges of
the primary index, to support the original assertion.

Fixes cockroachdb#93703
Fixes cockroachdb#93708
Epic: none

pkg/cmd/roachtest/tests/copy.go

@@ -71,7 +71,7 @@ func registerCopy(r registry.Registry) {
 
 			rangeCount := func() int {
 				var count int
-				const q = "SELECT count(*) FROM [SHOW RANGES FROM TABLE bank.bank]"
+				const q = "SELECT count(*) FROM [SHOW RANGES FROM INDEX bank.bank@primary]"
 				if err := db.QueryRow(q).Scan(&count); err != nil {
 					t.Fatalf("failed to get range count: %v", err)
 				}