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

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `clang-tools-extra` at step 2 "checkout".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/11723

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 2 (checkout) failure: update (failure)
...
remote: Counting objects:  76% (65/85)        
remote: Counting objects:  77% (66/85)        
remote: Counting objects:  78% (67/85)        
remote: Counting objects:  80% (68/85)        
remote: Counting objects:  81% (69/85)        
remote: Counting objects:  82% (70/85)        
remote: Counting objects:  83% (71/85)        
remote: Counting objects:  84% (72/85)        
remote: Counting objects:  85% (73/85)        
remote: Counting objects:  87% (74/85)        
remote: Counting objects:  88% (75/85)        
remote: Counting objects:  89% (76/85)        
remote: Counting objects:  90% (77/85)        
remote: Counting objects:  91% (78/85)        
remote: Counting objects:  92% (79/85)        
remote: Counting objects:  94% (80/85)        
remote: Counting objects:  95% (81/85)        
remote: Counting objects:  96% (82/85)        
remote: Counting objects:  97% (83/85)        
remote: Counting objects:  98% (84/85)        
remote: Counting objects: 100% (85/85)        
remote: Counting objects: 100% (85/85), done.        
remote: Compressing objects:   4% (1/23)        
remote: Compressing objects:   8% (2/23)        
remote: Compressing objects:  13% (3/23)        
remote: Compressing objects:  17% (4/23)        
remote: Compressing objects:  21% (5/23)        
remote: Compressing objects:  26% (6/23)        
remote: Compressing objects:  30% (7/23)        
remote: Compressing objects:  34% (8/23)        
remote: Compressing objects:  39% (9/23)        
remote: Compressing objects:  43% (10/23)        
remote: Compressing objects:  47% (11/23)        
remote: Compressing objects:  52% (12/23)        
remote: Compressing objects:  56% (13/23)        
remote: Compressing objects:  60% (14/23)        
remote: Compressing objects:  65% (15/23)        
remote: Compressing objects:  69% (16/23)        
remote: Compressing objects:  73% (17/23)        
remote: Compressing objects:  78% (18/23)        
remote: Compressing objects:  82% (19/23)        
remote: Compressing objects:  86% (20/23)        
remote: Compressing objects:  91% (21/23)        
remote: Compressing objects:  95% (22/23)        
remote: Compressing objects: 100% (23/23)        
remote: Compressing objects: 100% (23/23), done.        
remote: Total 25 (delta 20), reused 4 (delta 2), pack-reused 0 (from 0)        
>From https://github.com/llvm/llvm-project
 * branch                      main       -> FETCH_HEAD
fatal: reference is not a tree: d2d5203bf48af9b55b8e379c1c152fec97349340

```

</details>

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