Update assert messages format to be compliant with JUnitTestRunner and GradleTestRunner

[keytronic]

Currently assert messages match this regex expected: (.*)\s*but was: (.*) which is compliant with the JUnitTestRunner but not with the GradleTestRunner.

I propose to change regex to \nexpected: (.*)\n\s*got: (.*).
This way IDEA will be able to enable diff feature no matter which runner you use.

JUnitTestRunner available regexes
GradleTestRunner available regexes

[codecov]

Codecov Report

Merging #7345 (b97ce8d) into 3.x (6cc3a3b) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##                3.x    #7345      +/-   ##
============================================
+ Coverage     99.52%   99.53%   +0.01%     
  Complexity     6781     6781              
============================================
  Files           751      751              
  Lines         47482    47482              
  Branches       6378     6378              
============================================
+ Hits          47258    47263       +5     
+ Misses           99       98       -1     
+ Partials        125      121       -4     

Impacted Files	Coverage Δ
.../reactivex/rxjava3/observers/BaseTestConsumer.java	100.00% <100.00%> (ø)
.../operators/flowable/FlowableBlockingSubscribe.java	93.02% <0.00%> (-4.66%)	⬇️
...l/operators/observable/ObservableFlatMapMaybe.java	92.95% <0.00%> (-4.23%)	⬇️
...o/reactivex/rxjava3/processors/AsyncProcessor.java	97.91% <0.00%> (-2.09%)	⬇️
...nternal/operators/parallel/ParallelSortedJoin.java	98.49% <0.00%> (-1.51%)	⬇️
...rnal/operators/flowable/FlowableFlatMapSingle.java	94.18% <0.00%> (-1.17%)	⬇️
...a3/internal/operators/flowable/FlowableReplay.java	98.92% <0.00%> (-0.86%)	⬇️
.../operators/observable/ObservableCombineLatest.java	99.38% <0.00%> (-0.62%)	⬇️
...a/io/reactivex/rxjava3/subjects/ReplaySubject.java	99.16% <0.00%> (-0.42%)	⬇️
...ternal/operators/observable/ObservableFlatMap.java	97.87% <0.00%> (-0.36%)	⬇️
... and 13 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6cc3a3b...b97ce8d. Read the comment docs.