Upgrade to a Java 11 baseline

[jponge]

Fixes #846
Fixes #847

[cescoffier]

Yeah!

[codecov]

Codecov Report

Merging #931 (55605eb) into main (78fb16b) will increase coverage by 0.03%.
The diff coverage is n/a.

❗ Current head 55605eb differs from pull request most recent head 6c75aa5. Consider uploading reports for the commit 6c75aa5 to get more accurate results

@@             Coverage Diff              @@
##               main     #931      +/-   ##
============================================
+ Coverage     88.86%   88.89%   +0.03%     
- Complexity     3085     3088       +3     
============================================
  Files           391      391              
  Lines         12500    12499       -1     
  Branches       1590     1590              
============================================
+ Hits          11108    11111       +3     
- Misses          736      742       +6     
+ Partials        656      646      -10     

Impacted Files	Coverage Δ
...perators/multi/processors/SerializedProcessor.java	75.24% <0.00%> (-9.91%)	⬇️
...allrye/mutiny/operators/uni/UniAndCombination.java	88.23% <0.00%> (-0.99%)	⬇️
...tiny/operators/multi/MultiBufferWithTimeoutOp.java	74.78% <0.00%> (-0.85%)	⬇️
...mallrye/mutiny/operators/multi/MultiFlatMapOp.java	84.19% <0.00%> (-0.31%)	⬇️
...y/operators/multi/replay/AppendOnlyReplayList.java	92.30% <0.00%> (-0.12%)	⬇️
...a/io/smallrye/mutiny/helpers/BlockingIterable.java	87.03% <0.00%> (+0.92%)	⬆️
...java/io/smallrye/mutiny/helpers/Subscriptions.java	80.11% <0.00%> (+1.10%)	⬆️
...subscription/SwitchableSubscriptionSubscriber.java	95.20% <0.00%> (+1.60%)	⬆️
...io/smallrye/mutiny/operators/uni/UniMemoizeOp.java	91.26% <0.00%> (+1.94%)	⬆️
...operators/multi/builders/CollectionBasedMulti.java	96.77% <0.00%> (+3.22%)	⬆️
... and 2 more