docs(datafusion): update website link (#9072)

With DataFusion [now being a top-level
project](apache/datafusion#9691 (comment)),
this URL now redirects, and I have updated it to point to the new site.

https://arrow.apache.org/datafusion

https://datafusion.apache.org/

Author: IndexSeek

docs/backends/datafusion.qmd

@@ -1,6 +1,6 @@
 # DataFusion
 
-[https://arrow.apache.org/datafusion](https://arrow.apache.org/datafusion)
+[https://datafusion.apache.org/](https://datafusion.apache.org/)
 
 ![](https://img.shields.io/badge/memtables-not supported- grey?style=flat-square) ![](https://img.shields.io/badge/inputs-CSV | Delta Lake | Parquet-blue?style=flat-square) ![](https://img.shields.io/badge/outputs-CSV | Delta Lake | pandas | Parquet | PyArrow-orange?style=flat-square)