[clang] Improve error message for invalid lambda captures (PR #94865)

[via cfe-commits]

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@@ -623,6 +623,8 @@ Improvements to Clang's diagnostics
 - Clang no longer emits a "declared here" note for a builtin function that has no declaration in source.
   Fixes #GH93369.
 
+- Clang now has an improved error message when trying to capture a class member variable for lambda function expressions.
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Sirraide wrote:

```suggestion
- Clang now has an improved error message for captures that refer to a class member.
  Fixes #GH94764.
```

https://github.com/llvm/llvm-project/pull/94865