[clang] [clang][Sema] Simplify err_init_conversion_failed diagnostic message for const variables (PR #82109)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! I had an idea that might be an improved approach, but the general idea of the patch is great. I think this can likely land without a change to `clang/docs/ReleaseNotes.rst` because it's a minor wording improvement, but you can feel free to add a release note if you'd like.

https://github.com/llvm/llvm-project/pull/82109