[clang] [analyzer] Update the undefined assignment checker diagnostics to not use the term 'garbage' (PR #126596)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

Thanks for the update, I'm merging the commit.

By the way, Github also has built-in support for viewing the before-the-edit version of the PR description:
![image](https://github.com/user-attachments/assets/58213a41-ce76-4e1a-a850-7d4225cdd3e3)


https://github.com/llvm/llvm-project/pull/126596