Get rid of FutureWarnings related to Model.initial_point

[ricardoV94]

Also closes #5247

[codecov]

Codecov Report

Merging #5273 (c1bc2bd) into main (cf95a78) will decrease coverage by 0.01%.
The diff coverage is 80.64%.

@@            Coverage Diff             @@
##             main    #5273      +/-   ##
==========================================
- Coverage   78.99%   78.97%   -0.02%     
==========================================
  Files          87       87              
  Lines       14350    14351       +1     
==========================================
- Hits        11336    11334       -2     
- Misses       3014     3017       +3     

Impacted Files	Coverage Δ
pymc/sampling_jax.py	0.00% <0.00%> (ø)
pymc/backends/base.py	86.25% <50.00%> (ø)
pymc/tests/models.py	87.76% <80.00%> (ø)
pymc/model.py	82.99% <100.00%> (-0.28%)	⬇️
pymc/step_methods/hmc/base_hmc.py	91.12% <100.00%> (ø)
pymc/step_methods/metropolis.py	82.83% <100.00%> (ø)
pymc/step_methods/mlda.py	96.38% <100.00%> (ø)

[michaelosthege]

Thanks!