docs: Note pyiceberg only works with datafusion < 49 (#2602)

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# Rationale for this change

[Datafusion >= 49 is not backward
compatible](apache/iceberg-rust#1647 (comment))
and [Datafusion
API](https://py.iceberg.apache.org/api/#apache-datafusion) fails with
`bus error`.

This also fixes trailing whitespace in index.md.

## Are these changes tested?
Doc changes.

## Are there any user-facing changes?
No.
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Author: manuzhang

mkdocs/docs/api.md

@@ -1939,7 +1939,7 @@ PyIceberg integrates with [Apache DataFusion](https://datafusion.apache.org/) th
 
     The integration has a few caveats:
 
-    - Only works with `datafusion >= 45`
+    - Only works with `datafusion >= 45, < 49`
     - Depends directly on `iceberg-rust` instead of PyIceberg's implementation
     - Has limited features compared to the full PyIceberg API