minor: Fix an example in the PruningPredicate documentation (apache#18742)

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## Rationale for this change

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I noticed one rewritten predicate in the `PruningPredicate`
documentation might not be correct.

I have tried with example
`datafusion/datafusion-examples/examples/query_planning/pruning.rs` to
generate the rewritten predicate to confirm it:
`x<5: x_null_count@1 != row_count@2 AND x_min@0 < 5`

### Fun side story

I came across a thread on V2EX (a Chinese technical-ish community)
titled “Have you ever read a technical book that felt truly satisfying?”

Someone replied with a very specific section from the DataFusion
documentation comment (the one this PR updates)
<img width="964" height="155" alt="image"
src="https://github.com/user-attachments/assets/c3c5f7f5-1b01-4cc6-ad96-8ab59560db24"
/>

I’ve read it — and it’s true 😆 , truly satisfying. I believe @alamb
originally wrote it.

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Author: 2010YOUY01

datafusion/pruning/src/pruning_predicate.rs

@@ -238,7 +238,7 @@ use datafusion_physical_plan::{ColumnarValue, PhysicalExpr};
 /// Original Predicate | Rewritten Predicate
 /// ------------------ | --------------------
 /// `x = 5` | `x_null_count != x_row_count AND (x_min <= 5 AND 5 <= x_max)`
-/// `x < 5` | `x_null_count != x_row_count THEN false (x_max < 5)`
+/// `x < 5` | `x_null_count != x_row_count AND (x_min < 5)`
 /// `x = 5 AND y = 10` | `x_null_count != x_row_count AND (x_min <= 5 AND 5 <= x_max) AND y_null_count != y_row_count (y_min <= 10 AND 10 <= y_max)`
 /// `x IS NULL`  | `x_null_count > 0`
 /// `x IS NOT NULL`  | `x_null_count != row_count`