fix: allow fork PRs to post review suggestions in lint workflow

Use pull_request_target to enable write access for fork PRs.
Upgrade actions/checkout to v4 and actions/setup-python to v5
to address Node.js 20 deprecation warning.

Author: Jonathan Visser

.github/workflows/lint.yaml

@@ -1,7 +1,7 @@
 name: Run linting and suggest changes
 
 on:
-  pull_request:
+  pull_request_target:
 
 permissions:
   contents: read
@@ -15,8 +15,10 @@ jobs:
         python-version: ['3.12']
 
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-python@v4
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies