Fix conditional posterior shape and device bugs.

[janfb]

There were a couple of bugs when using the MCMCPosterior with a conditioned_potential, which are fixed in this PR.

fixes #1364

[michaeldeistler]

LGTM, thanks!

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 78.41%. Comparing base (d3f22b5) to head (48747f0).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
...inference/potentials/likelihood_based_potential.py	42.85%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1373       +/-   ##
===========================================
- Coverage   89.40%   78.41%   -11.00%     
===========================================
  Files         118      118               
  Lines        8715     8784       +69     
===========================================
- Hits         7792     6888      -904     
- Misses        923     1896      +973     

Flag	Coverage Δ
unittests	78.41% <42.85%> (-11.00%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sbi/utils/sbiutils.py	78.11% <ø> (-8.68%)	⬇️
...inference/potentials/likelihood_based_potential.py	68.13% <42.85%> (-31.87%)	⬇️

... and 32 files with indirect coverage changes