Diamond operators in tests, small packages

[dvolkovv]

Hello, in this pull request i've changed all IDE marked explicit types with diamond operator. Affected packages is in tests root.

There is one test fail in CompletableTest.repeatNormal , but diamond is not the cause, there is last stack entry:
java.lang.AssertionError: expected:<6> but was:<5>
at org.junit.Assert.fail(Assert.java:88)

This PR is part of #6767 issue resolving.

[codecov]

Codecov Report

Merging #6789 into 3.x will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                3.x    #6789      +/-   ##
============================================
- Coverage     98.24%   98.21%   -0.03%     
+ Complexity     6286     6281       -5     
============================================
  Files           696      696              
  Lines         45390    45390              
  Branches       6233     6233              
============================================
- Hits          44592    44582      -10     
- Misses          277      285       +8     
- Partials        521      523       +2

Impacted Files	Coverage Δ	Complexity Δ
...ctivex/rxjava3/internal/util/QueueDrainHelper.java	95.83% <0%> (-4.17%)	55% <0%> (-3%)
...eactivex/rxjava3/processors/BehaviorProcessor.java	96.58% <0%> (-2.44%)	51% <0%> (ø)
.../operators/observable/ObservableFlatMapSingle.java	90.47% <0%> (-2.39%)	2% <0%> (ø)
.../internal/disposables/ListCompositeDisposable.java	98% <0%> (-2%)	34% <0%> (-1%)
...rnal/operators/observable/ObservableSwitchMap.java	91.57% <0%> (-1.58%)	3% <0%> (ø)
...ava3/internal/operators/parallel/ParallelJoin.java	91.66% <0%> (-1.52%)	3% <0%> (ø)
...ava3/internal/operators/maybe/MaybeMergeArray.java	96.04% <0%> (-1.13%)	6% <0%> (ø)
...3/internal/operators/flowable/FlowablePublish.java	97.53% <0%> (-0.99%)	16% <0%> (-1%)
...operators/observable/ObservableMergeWithMaybe.java	99.09% <0%> (-0.91%)	2% <0%> (ø)
.../operators/maybe/MaybeFlatMapIterableFlowable.java	95.9% <0%> (-0.82%)	2% <0%> (ø)
... and 8 more

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