DOC: fix docstring of DataFrame.to_latex, double curly braces to single
The parameters docstring of [`to_latex`](https://pandas.pydata.org/docs/dev/reference/api/pandas.DataFrame.to_latex.html) is misleading. For example, `float_format="{{:0.2f}}".format` should rather use single curly brace, as the example in the docstring

```py
>>> df = pd.DataFrame(dict(name=['Raphael', 'Donatello'],
...                        age=[26, 45],
...                        height=[181.23, 177.65]))
>>> print(df.to_latex(index=False,
...                   formatters={"name": str.upper},
...                   float_format="{:.1f}".format,
...                   ))  
\begin{tabular}{lrr}
\toprule
name & age & height \\
\midrule
RAPHAEL & 26 & 181.2 \\
DONATELLO & 45 & 177.7 \\
\bottomrule
\end{tabular}
```

This PR replaces {{}} with {} in `to_latex` docstring.

- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Thanks @yuanx749 