Fix DiscreteUniformRV dropping degenerate dimension

[ricardoV94]

What is this PR about?

Bug found by @drbenvincent
Scipy does not respect degenerate dimensions (size=1) implied by the parameters

Checklist

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• Make sure that the pre-commit linting/style checks pass.
• Link relevant issues (preferably in nice commit messages)
• Are the changes covered by tests and docstrings?
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Major / Breaking Changes

• ...

Bugfixes / New features

• Fix bug where DiscreteUniformRV would drop degenerate dimensions from draws

Docs / Maintenance

• ...

[codecov]

Codecov Report

Merging #6151 (588b72d) into main (75e9406) will increase coverage by 2.14%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6151      +/-   ##
==========================================
+ Coverage   87.14%   89.29%   +2.14%     
==========================================
  Files          91       91              
  Lines       20717    20720       +3     
==========================================
+ Hits        18054    18501     +447     
+ Misses       2663     2219     -444     

Impacted Files	Coverage Δ
pymc/distributions/discrete.py	99.21% <100.00%> (ø)
pymc/tests/distributions/test_discrete.py	98.88% <100.00%> (+<0.01%)	⬆️
pymc/parallel_sampling.py	85.80% <0.00%> (-1.00%)	⬇️
pymc/backends/base.py	86.44% <0.00%> (+0.73%)	⬆️
pymc/step_methods/hmc/quadpotential.py	73.76% <0.00%> (+0.74%)	⬆️
pymc/printing.py	86.08% <0.00%> (+0.86%)	⬆️
pymc/step_methods/slicer.py	96.20% <0.00%> (+1.26%)	⬆️
pymc/backends/report.py	91.04% <0.00%> (+4.47%)	⬆️
pymc/step_methods/arraystep.py	94.32% <0.00%> (+7.80%)	⬆️
pymc/sampling.py	82.19% <0.00%> (+12.08%)	⬆️
... and 2 more

[ricardoV94]

Failing test is fixed by #6160