Fix off-by-one retry count when using exponential backoff

[cescoffier]

Fix #675.

[codecov]

Codecov Report

Merging #678 (4448517) into main (36c5c3b) will increase coverage by 0.13%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main     #678      +/-   ##
============================================
+ Coverage     90.06%   90.19%   +0.13%     
  Complexity     2985     2985              
============================================
  Files           374      374              
  Lines         11764    11764              
  Branches       1476     1478       +2     
============================================
+ Hits          10595    10611      +16     
+ Misses          600      590      -10     
+ Partials        569      563       -6     

Impacted Files	Coverage Δ
...io/smallrye/mutiny/helpers/ExponentialBackoff.java	81.81% <100.00%> (ø)
...ava/io/smallrye/mutiny/helpers/HalfSerializer.java	77.77% <0.00%> (-11.12%)	⬇️
...subscription/SwitchableSubscriptionSubscriber.java	95.08% <0.00%> (-2.46%)	⬇️
.../io/smallrye/mutiny/helpers/queues/DrainUtils.java	84.44% <0.00%> (-2.23%)	⬇️
...java/io/smallrye/mutiny/helpers/Subscriptions.java	80.11% <0.00%> (-1.66%)	⬇️
...mallrye/mutiny/helpers/queues/MpscLinkedQueue.java	96.77% <0.00%> (-1.62%)	⬇️
...mallrye/mutiny/operators/multi/MultiFlatMapOp.java	86.29% <0.00%> (+0.62%)	⬆️
...lrye/mutiny/subscription/SerializedSubscriber.java	88.67% <0.00%> (+0.94%)	⬆️
...smallrye/mutiny/operators/multi/MultiEmitOnOp.java	90.47% <0.00%> (+0.95%)	⬆️
...allrye/mutiny/operators/uni/UniAndCombination.java	89.53% <0.00%> (+1.16%)	⬆️
... and 4 more