ci: Checkout latest merged pulls

Github-Pull: #33303
Rebased-From: fa8f081af31

.github/workflows/ci.yml

@@ -123,8 +123,12 @@ jobs:
       BASE_ROOT_DIR: ${{ github.workspace }}
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
+      - &CHECKOUT
+        name: Checkout
+        uses: actions/checkout@v5
+        with:
+          # Ensure the latest merged pull request state is used, even on re-runs.
+          ref: &CHECKOUT_REF_TMPL ${{ github.event_name == 'pull_request' && github.ref || '' }}
 
       - name: Clang version
         run: |
@@ -192,8 +196,7 @@ jobs:
             job-name: 'Win64 native fuzz, VS 2022'
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
+      - *CHECKOUT
 
       - name: Configure Developer Command Prompt for Microsoft Visual C++
         # Using microsoft/setup-msbuild is not enough.
@@ -370,8 +373,7 @@ jobs:
             file-env: './ci/test/00_setup_env_native_msan.sh'
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@v5
+      - *CHECKOUT
 
       - name: Configure environment
         uses: ./.github/actions/configure-environment
@@ -414,6 +416,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v5
         with:
+          ref: *CHECKOUT_REF_TMPL
           fetch-depth: 0
 
       - name: Configure Docker