Windows cannot generate docs correctly for source-lit. All files simply have a file path as their contents.

@Felonious-Spellfire is already working on this.

Since Sep 15, 2022.

## 🐛 Bug

When generating the docs for Windows 11 or conda Windows machines, the contents of the HTML output is a file path. No other content appears in any of the HTML files (only a file path).

### To Reproduce

The results are the same using a Windows 11 host or a conda Windows machine with the following versions of Python: 3.8, 3.9, 3.10.

1. Clone the Lightning repo
2. In the root directory run the following:
pip install -r requirements/app/docs.txt -U
pip install -e .
3. Run this command:
set PL_FAST_DOCS_DEV=1
4. Run the following command to generate docs:
python -m sphinx -b html -W --keep-going docs/source-lit docs/build

Generation completes with an error (the same error that appears on a conda Ubuntu generation).
5. Go to the build directory and open the index.html file (or any file in the build directory) and the contents of the file is simply a file path.

### Expected behavior

The output generated is the same as that for an Ubuntu generation (meaning that the HTML output is correct for each file and not simply a file path.

### Environment

The results are the same using a Windows 11 host or a conda Windows machine with the following versions of Python: 3.8, 3.9, 3.10.

Generating the output on a conda Ubuntu machine with Python: 3.8, 3.9, 3.10 generates correctly.

cc @borda @rohitgr7 @Felonious-Spellfire