TST: Fix for doctest in style_render.py -> pandas.io.formats.style_re…
This pull request fixes the doctest pandas.io.formats.style_render.StylerRenderer.format

- [X] closes #42766 

Following this commit, all the doctests in style_render.py file passed.

Output:
```
python -m pytest --doctest-modules pandas/io/formats/style_render.py
========================================================= test session starts =========================================================
platform linux -- Python 3.8.5, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
rootdir: /home/aneesh/Desktop/Side Projects/ops/pandas, configfile: pyproject.toml
plugins: forked-1.3.0, asyncio-0.15.1, anyio-3.3.0, cov-2.12.1, instafail-0.4.2, hypothesis-6.14.3, xdist-2.3.0
collected 3 items                                                                                                                     

pandas/io/formats/style_render.py ...

--------------------------- generated xml file: /home/aneesh/Desktop/Side Projects/ops/pandas/test-data.xml ---------------------------
======================================================== slowest 30 durations =========================================================
1.06s call     pandas/io/formats/style_render.py::pandas.io.formats.style_render.StylerRenderer.format

(8 durations < 0.005s hidden.  Use -vv to show these durations.)
========================================================== 3 passed in 1.15s ==========================================================

```
