models/MontagueDayanSejnowski: Use versioned seaborn style

[jvesely]

Plain names are deprecated in matplotlib and removed in matplotlib==3.8.0.
The versioned name with underscore was introduced in matplotlib==3.7.0, 6608eedfc6f33f723f1e13c6025a5b918c7c9f6d
("Re-rename builtin seaborn styles to not include a dot.")

[github-actions]

This PR causes the following changes to the html docs (ubuntu-latest-3.11):

diff -r docs-base/TransferFunctions.html docs-head/TransferFunctions.html
2562c2562
< <p><a class="reference internal" href="TimerFunctions.html#psyneulink.core.components.functions.nonstateful.timerfunctions.AsymptoticTimer.bounds" title="psyneulink.core.components.functions.nonstateful.timerfunctions.AsymptoticTimer.bounds"><code class="xref any py py-attr docutils literal notranslate"><span class="pre">bounds</span></code></a> – specifies the lower and upper limits of the result;  if there are none, the attribute is set to
---
> <p><a class="reference internal" href="OptimizationFunctions.html#psyneulink.core.components.functions.optimizationfunctions.GradientOptimization.bounds" title="psyneulink.core.components.functions.optimizationfunctions.GradientOptimization.bounds"><code class="xref any py py-attr docutils literal notranslate"><span class="pre">bounds</span></code></a> – specifies the lower and upper limits of the result;  if there are none, the attribute is set to
diff -r docs-base/_downloads/a4d0d527489dd865a0d84206f08d9c31/MontagueDayanSejnowski96.py docs-head/_downloads/a4d0d527489dd865a0d84206f08d9c31/MontagueDayanSejnowski96.py
116c116
<         with plt.style.context('seaborn'):
---
>         with plt.style.context('seaborn-v0_8'):
179c179
<         with plt.style.context('seaborn'):
---
>         with plt.style.context('seaborn-v0_8'):
243c243
<         with plt.style.context('seaborn'):
---
>         with plt.style.context('seaborn-v0_8'):

...

See CI logs for the full diff.