Raise per-user client limit in tests that use more than 2 client IDs

Tests for update counting and stale compaction use 4 client IDs from the
same user, which now exceeds the DEFAULT_MAX_CLIENTS_PER_USER limit of 2
introduced in the peer limits backport.

Author: pkevan

tests/phpunit/tests/rest-api/rest-sync-server.php

@@ -530,6 +530,14 @@ public function test_sync_update_data_preserved() {
 	public function test_sync_total_updates_increments() {
 		wp_set_current_user( self::$editor_id );
 
+		// Raise per-user client limit so 4 clients from one user are allowed.
+		add_filter(
+			'real_time_collaboration_max_clients_per_user',
+			function () {
+				return 10;
+			}
+		);
+
 		$room   = $this->get_post_room();
 		$update = array(
 			'type' => 'update',
@@ -651,6 +659,14 @@ public function test_sync_should_compact_is_false_for_non_compactor() {
 	public function test_sync_stale_compaction_succeeds_when_newer_compaction_exists() {
 		wp_set_current_user( self::$editor_id );
 
+		// Raise per-user client limit so 4 clients from one user are allowed.
+		add_filter(
+			'real_time_collaboration_max_clients_per_user',
+			function () {
+				return 10;
+			}
+		);
+
 		$room   = $this->get_post_room();
 		$update = array(
 			'type' => 'update',