Rollup merge of rust-lang#75424 - joseluis:patch-1, r=joshtriplett

fix wrong word in documentation

Change "two" to "three", since there are three significantly different things printed below that sentence:

---

While these:
```rust
println!("{}, `{name:.*}` has 3 fractional digits", "Hello", 3, name=1234.56);
println!("{}, `{name:.*}` has 3 characters", "Hello", 3, name="1234.56");
println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");
```

print two significantly different things:

``` rust
Hello, `1234.560` has 3 fractional digits
Hello, `123` has 3 characters
Hello, `     123` has 3 right-aligned characters
```
---
[`https://doc.rust-lang.org/std/fmt/#precision`](https://doc.rust-lang.org/std/fmt/#precision)

Author: JohnTitor

library/alloc/src/fmt.rs

@@ -239,7 +239,7 @@
 //! println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");
 //! ```
 //!
-//! print two significantly different things:
+//! print three significantly different things:
 //!
 //! ```text
 //! Hello, `1234.560` has 3 fractional digits