Exclude code blocks that aren't run

[LiamConnors]

In the docs we have Python code which is formatted as Python code

but not run. In the Markdown it looks like this, it's inside blocks:

<!-- #region -->
Code that relied on the `add_*` methods to return a reference to the newly created trace will need to be updated to access the trace from the returned figure.  This can be done by appending `.data[-1]` to the add trace expression.

Here is an example of a version 3 code snippet that adds a scatter trace to a figure, assigns the result to a variable named `scatter`, and then modifies the marker size of the scatter trace.

```python
import plotly.graph_objs as go
fig = go.Figure()
scatter = fig.add_trace(go.Scatter(y=[2, 3, 1]))
scatter.marker.size = 20

In version 4, this would be replaced with the following:

import plotly.graph_objects as go
fig = go.Figure()
scatter = fig.add_trace(go.Scatter(y=[2, 3, 1])).data[-1]
scatter.marker.size = 20

This PR modifies the `run_markdown.py` script to not run these sections. 
Also updates the test script to use the same function as `run_markdown.py` uses