ci: Support bot PRs by adding pull_request_target trigger

Add pull_request_target event to run CI on PRs from bots (like
pre-commit.ci) and forks. Update checkout steps to use the PR head
SHA to ensure the actual PR code is tested.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: tablackburn

.github/workflows/CI.yaml

@@ -5,6 +5,8 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
+  pull_request_target:
+    branches: [main]
 
 permissions:
   contents: read
@@ -16,6 +18,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: Cache PowerShell modules
         uses: actions/cache@v5
@@ -59,6 +63,8 @@ jobs:
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
       - uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
 
       - name: Cache PowerShell modules
         uses: actions/cache@v5