chore: bump GitHub Actions to latest versions

- actions/checkout v4 → v6
- actions/setup-node v4 → v6
- actions/github-script v7 → v8
- actions/setup-dotnet v4 → v5

Author: Ufuk Cetinkaya

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup Flutter
         uses: subosito/flutter-action@v2

.github/workflows/pr-review.yml

@@ -12,7 +12,7 @@ jobs:
       pull-requests: write
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Label PR by size
         uses: codelytv/pr-size-labeler@v1
@@ -30,7 +30,7 @@ jobs:
           fail_if_xl: false
 
       - name: Check PR description
-        uses: actions/github-script@v7
+        uses: actions/github-script@v8
         with:
           script: |
             const pr = context.payload.pull_request;