3.x: Do not update snapshot Javadocs from secondary branches

[akarnokd]

This PR changes buildViaTravis.sh to not publish a snapshot for branches other than 3.x and push_javadoc.sh to not upload the generated javadocs for branches other than 3.x.

This will prevent the unnecessary uploads when Dependabot creates a new bump branch.

[codecov]

Codecov Report

Merging #6752 into 3.x will increase coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                3.x    #6752      +/-   ##
============================================
+ Coverage     98.11%   98.17%   +0.05%     
- Complexity     6187     6191       +4     
============================================
  Files           677      677              
  Lines         44626    44626              
  Branches       6161     6161              
============================================
+ Hits          43787    43812      +25     
+ Misses          299      291       -8     
+ Partials        540      523      -17

Impacted Files	Coverage Δ	Complexity Δ
...java3/internal/observers/FutureSingleObserver.java	94.33% <0%> (-3.78%)	24% <0%> (-1%)
...ernal/operators/flowable/FlowableFlatMapMaybe.java	95.31% <0%> (-1.05%)	2% <0%> (ø)
...nternal/operators/observable/ObservableCreate.java	98.29% <0%> (-0.86%)	2% <0%> (ø)
...perators/single/SingleFlatMapIterableFlowable.java	95.83% <0%> (-0.84%)	2% <0%> (ø)
...a/io/reactivex/rxjava3/subjects/ReplaySubject.java	97.09% <0%> (-0.42%)	50% <0%> (ø)
...a3/internal/operators/flowable/FlowableCreate.java	97.73% <0%> (+0.32%)	6% <0%> (ø)	⬇️
...ternal/operators/flowable/FlowableWindowTimed.java	93.25% <0%> (+0.46%)	4% <0%> (ø)	⬇️
...ternal/operators/observable/ObservableGroupBy.java	95.08% <0%> (+0.54%)	2% <0%> (ø)	⬇️
...operators/observable/ObservableMergeWithMaybe.java	100% <0%> (+0.9%)	2% <0%> (ø)	⬇️
...3/internal/operators/flowable/FlowablePublish.java	98.52% <0%> (+0.98%)	17% <0%> (+1%)	⬆️
... and 10 more

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