docs: Use pattern rule to execute generator scripts

[jvesely]

find -exec does not propagate errors.

[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
2365c2365
< <p><a class="reference internal" href="#psyneulink.core.components.functions.transferfunctions.Exponential.bounds" title="psyneulink.core.components.functions.transferfunctions.Exponential.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

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[github-actions]

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

No differences!

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