[llvm] [llvm] Proofread ProgrammersManual.rst (PR #151853)

[Tim Gymnich via llvm-commits]

================
@@ -3853,13 +3853,13 @@ Important Subclasses of Constant
     value of this constant, an APInt value.
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tgymnich wrote:

```suggestion
    value of this constant, an ``APInt`` value.
```

https://github.com/llvm/llvm-project/pull/151853