DOC: Fix typo of `=!` to `!=` in docstring
This fixes GH36075.

- [x] closes #36075 

I'm marking the following list items as not-applicable because I'm simply swapping two characters in a docstring that had been in the incorrect order.

- [NA] tests added / passed
- [NA] passes `black pandas`
- [NA] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [NA] whatsnew entry

Thanks @daytonb ! Thanks! It's been a pleasure. Thanks for the quick merge. So this change actually breaks building docs, at least using sphinx. Leads to an error

```
/usr/local/lib/python3.8/site-packages/docutils/nodes.py", line 567, in __getitem__
    return self.attributes[key]
KeyError: 'reftarget'
```

whereas simply swapping them back fixes the problem. Any idea what might be going on here? Is no one else gets to it before me I could look into it, but probably not
until tomorrow.


On Fri, Apr 2, 2021 at 7:34 PM Sami Jawhar ***@***.***> wrote:

> So this change actually breaks building docs, at least using sphinx. Leads
> to an error
>
> /usr/local/lib/python3.8/site-packages/docutils/nodes.py", line 567, in __getitem__
>     return self.attributes[key]
> KeyError: 'reftarget'
>
> whereas simply swapping them back fixes the problem. Any idea what might
> be going on here?
>
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>
 @sjawhar, can you give me the steps you ran to reproduce this issue? It seams unlikely that my text change could lead to the error you posted. Also, when I my docstring change is already part of the current (v1.2.3) release and the documentation is rendered properly online, all of which seems to indicate that this docstring change isn't the cause of the issue you're reporting. If you can give me some steps to reproduce, I'd be happy to try to figure out what's going on.