3.x: Fix Observable amb, combineLatest & zip ArrayStoreException

[akarnokd]

When using iterable of sources, the initial array is the wrong type and causes ArrayStoreException.

Unit tests were added to verify the other implementations.

Fixes #6753

[codecov]

Codecov Report

Merging #6756 into 3.x will decrease coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##                3.x   #6756      +/-   ##
===========================================
- Coverage     98.13%   98.1%   -0.04%     
+ Complexity     6190    6186       -4     
===========================================
  Files           677     677              
  Lines         44626   44626              
  Branches       6161    6161              
===========================================
- Hits          43794   43780      -14     
- Misses          300     303       +3     
- Partials        532     543      +11

Impacted Files	Coverage Δ	Complexity Δ
.../operators/observable/ObservableCombineLatest.java	96.81% <100%> (ø)	6 <0> (ø)	⬇️
...3/internal/operators/observable/ObservableZip.java	100% <100%> (ø)	6 <0> (ø)	⬇️
...3/internal/operators/observable/ObservableAmb.java	98.94% <100%> (ø)	8 <0> (ø)	⬇️
...l/operators/observable/ObservableFlatMapMaybe.java	83.8% <0%> (-11.27%)	2% <0%> (ø)
...rnal/subscribers/SinglePostCompleteSubscriber.java	92.3% <0%> (-7.7%)	14% <0%> (-1%)
...rxjava3/internal/observers/QueueDrainObserver.java	97.43% <0%> (-2.57%)	21% <0%> (-1%)
.../internal/disposables/ListCompositeDisposable.java	98% <0%> (-2%)	34% <0%> (-1%)
...tivex/rxjava3/disposables/CompositeDisposable.java	98.14% <0%> (-1.86%)	39% <0%> (-1%)
...perators/single/SingleFlatMapIterableFlowable.java	94.16% <0%> (-1.67%)	2% <0%> (ø)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	92.7% <0%> (-1.05%)	2% <0%> (ø)
... and 10 more

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