chore(deps): update actions/checkout digest to b4ffde6 (#18)

Signed-off-by: Renovate Bot <bot@renovateapp.com>

.github/workflows/build-reference.yml

@@ -31,7 +31,7 @@ jobs:
           - wallaby
     steps:
       - name: Checkout code
-        uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
       - name: Install requirements
         run: pip install -r requirements.txt
       - name: Build documentation