[clang-tools-extra] [clangd] `--header-insertion` CLI fix (PR #146235)

[via cfe-commits]

MythreyaK wrote:

I tested these locally and seems to work as expected. Please do double-check, just in case I missed something!

|  config  |   cli      |    outcome     |
|----------|------------|----------------|
|  IWYU    |  iwyu      |  inserted      |
|  IWYU    |  never     |  not inserted  |
|  Never   |  iwyu      |  inserted      |
|  Never   |  never     |  not inserted  |
|  Never   |  [no opt]  |  not inserted  |
|  IWYU    |  [no opt]  |  inserted      |
| [no opt] |  iwyu      |  inserted      |
| [no opt] |  never     |  not inserted  |
| [no opt] |  [no opt]  |  inserted      |




https://github.com/llvm/llvm-project/pull/146235