ORC-1945: Update Python documentation with PyArrow 20.0.0 and Dask 2025.5.1

### What changes were proposed in this pull request?

This PR aims to update Python document with PyArrow 20.0.0 and Dask 2025.5.1.

### Why are the changes needed?

To provide an up-to-date Python documentation.

### How was this patch tested?

Manually tested with `Python 3.13.5`.

```
$ python3 --version
Python 3.13.5

$ ipython3
Python 3.13.5 (main, Jun 11 2025, 15:36:57) [Clang 17.0.0 (clang-1700.0.13.3)]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.3.0 -- An enhanced Interactive Python. Type '?' for help.
Tip: You can use `files = !ls *.png`

In [1]: ...
```

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #2311 from dongjoon-hyun/ORC-1945.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>
(cherry picked from commit 0f0273d)
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

site/_docs/dask.md

@@ -9,7 +9,7 @@ permalink: /docs/dask.html
 [Dask](https://dask.org) also supports Apache ORC.
 
 ```
-pip3 install "dask[dataframe]==2024.12.1"
+pip3 install "dask[dataframe]==2025.5.1"
 pip3 install pandas
 ```
 

site/_docs/pyarrow.md

@@ -9,7 +9,7 @@ permalink: /docs/pyarrow.html
 [Apache Arrow](https://arrow.apache.org) project's [PyArrow](https://pypi.org/project/pyarrow/) is the recommended package.
 
 ```
-pip3 install pyarrow==18.1.0
+pip3 install pyarrow==20.0.0
 pip3 install pandas
 ```