fix(scripts): drop the stale "five" from the balancing-pins banner (#17402)

The banner above the balancing-pins battery in
scripts/partition-test-shards.mjs said "These five pin the quantity
and the outcome" while six numbered pins (1-6) follow it. Make the
sentence numberless, matching the sibling banner at the
predicted-vs-measured battery ("These pin the one comparison..."),
so it cannot drift again when a seventh pin is added. No pin was
added, removed, or reordered; zero behaviour change.


Claude-Session: https://claude.ai/code/session_012GKcPZbMoGq7WPzKLfRBTU

Co-authored-by: Claude <noreply@anthropic.com>

Author: baozhoutao

scripts/partition-test-shards.mjs

@@ -820,7 +820,7 @@ function selfTest() {
   // Everything above pins that the split is a correct, deterministic, total
   // cover of its input. None of it noticed that the six bins it produced ran
   // 5.0/6.2/6.3/13.6/6.3/9.0 minutes, because a perfectly-balanced split of the
-  // WRONG quantity satisfies every one of those assertions. These five pin the
+  // WRONG quantity satisfies every one of those assertions. These pin the
   // quantity and the outcome.
   battery('the balancing pins (#10472)');