Allow the test trait to permit rethrown exceptions

[Firehed]

The main goal of this is to make it easy to implement handleException in v3.1 as a no-op rethrow without causing all of the trait-added tests to fail.

[codecov]

Codecov Report

Merging #63 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master      #63      +/-   ##
============================================
+ Coverage     96.11%   96.18%   +0.06%     
- Complexity      114      117       +3     
============================================
  Files            25       25              
  Lines           335      341       +6     
============================================
+ Hits            322      328       +6     
  Misses           13       13

Impacted Files	Coverage Δ	Complexity Δ
src/Traits/EndpointTestCases.php	94.44% <ø> (ø)	11 <0> (ø)	⬇️
src/Traits/HandlesOwnErrorsTestCases.php	100% <100%> (ø)	5 <4> (?)

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