chore: update to checkout@v4

Author: notmandatory

.github/workflows/publish-spm.yaml

@@ -17,14 +17,14 @@ jobs:
     runs-on: macos-12
     steps:
       - name: "Checkout build repo"
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: ${{ github.repository_owner }}/bdk-ffi
           path: build
           ref: ${{ inputs.ffitag }}
 
       - name: "Checkout dist repo"
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: dist