Fix #1461: test for bridge sampling

[arrjon]

Fixes issue #1461

The test failed too often, since the value which we compared to was unreliable. Now changed from harmonic mean sampling to laplace approximation.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.82%. Comparing base (f92fc8b) to head (9321ba9).

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1473      +/-   ##
===========================================
- Coverage    82.86%   82.82%   -0.04%     
===========================================
  Files          163      163              
  Lines        13760    13760              
===========================================
- Hits         11402    11397       -5     
- Misses        2358     2363       +5     

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[PaulJonasJost]

Tested locally, only failed 9 out of 100 times. Perhaps just for safety raise the flaky to 3 reruns? But probably not necessary.