IGNITE-23708 testAutomaticRebalanceIfMajorityIsLost is flaky

[JAkutenshi]

JIRA Ticket: IGNITE-23708

The goal

The main goal of the PR is to fix testAutomaticRebalanceIfMajorityIsLost:

1. Reset rebalance may be slower a little than expected 2s timeout on assertRealAssignments(node0, partId, 1) especially after IGNITE-22036 changes.
2. There is unnecessary planned rebalance with the same planned assignments as pending force reset assignments set equals to [1]. This leads also to a flacky non-null result on assertNull(getPendingAssignments(node0, partId)) check.

The reason

Tests shouldn't be flacky and flawed implementation should be fixed.

The solution

1. assertRealAssignments's timeout is increased up to 5s.
2. If during GroupUpdateRequest#partitionUpdate if there are alive nodes we have equal part and stable assignments we shouldn't schedule the redundant rebalance and then should put just null then.