[Github] Make code formatting action checkout SHA rather than ref

Checking out a ref of the branch requires the remote to be the same as
the fork whereas setting it to be the commit SHA allows for us to avoid
changing the remote. This should fix the action not working on PRs made
from forks (essentially all of them).

Author: boomanaiden154

.github/workflows/pr-code-format.yml

@@ -11,13 +11,13 @@ jobs:
       - name: Fetch LLVM sources
         uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.ref }}
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - name: Checkout through merge base
         uses: rmacklin/fetch-through-merge-base@v0
         with:
           base_ref: ${{ github.event.pull_request.base.ref }}
-          head_ref: ${{ github.event.pull_request.head.ref }}
+          head_ref: ${{ github.event.pull_request.head.sha }}
           deepen_length: 500
 
       - name: Get changed files