Fix incomplete AssertJ API usage

[jponge]

No description provided.

[codecov]

Codecov Report

Merging #531 (eb55d26) into main (425d20d) will increase coverage by 0.34%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main     #531      +/-   ##
============================================
+ Coverage     89.88%   90.23%   +0.34%     
- Complexity     3006     3016      +10     
============================================
  Files           382      382              
  Lines         11621    11621              
  Branches       1453     1455       +2     
============================================
+ Hits          10446    10486      +40     
+ Misses          597      578      -19     
+ Partials        578      557      -21     

Impacted Files	Coverage Δ	Complexity Δ
...perators/multi/processors/SerializedProcessor.java	92.07% <0.00%> (-1.00%)	26.00% <0.00%> (ø%)
...mallrye/mutiny/operators/multi/MultiFlatMapOp.java	85.04% <0.00%> (+0.31%)	3.00% <0.00%> (ø%)
...smallrye/mutiny/operators/multi/MultiEmitOnOp.java	90.47% <0.00%> (+0.95%)	2.00% <0.00%> (ø%)
...java/io/smallrye/mutiny/helpers/Subscriptions.java	81.76% <0.00%> (+1.10%)	50.00% <0.00%> (+1.00%)
...erators/multi/builders/SerializedMultiEmitter.java	83.54% <0.00%> (+1.26%)	27.00% <0.00%> (+1.00%)
...tiny/operators/multi/MultiBufferWithTimeoutOp.java	74.57% <0.00%> (+1.69%)	4.00% <0.00%> (ø%)
...subscription/SwitchableSubscriptionSubscriber.java	97.54% <0.00%> (+2.45%)	46.00% <0.00%> (+1.00%)
...io/smallrye/mutiny/operators/uni/UniMemoizeOp.java	95.04% <0.00%> (+3.96%)	28.00% <0.00%> (+2.00%)
.../io/smallrye/mutiny/helpers/queues/DrainUtils.java	80.00% <0.00%> (+4.44%)	12.00% <0.00%> (+1.00%)
...y/operators/multi/builders/IterableBasedMulti.java	88.29% <0.00%> (+6.38%)	4.00% <0.00%> (ø%)
... and 2 more