CI: Checkout libbase58/libblkmaker to test embedded-libraries build

Author: luke-jr

.github/workflows/build.yaml

@@ -16,7 +16,19 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
+      
+      - name: Checkout libbase58
+        uses: actions/checkout@v4
+        with:
+          repository: bitcoin/libbase58
+          path: libbase58
+      
+      - name: Checkout libblkmaker
+        uses: actions/checkout@v4
+        with:
+          repository: bitcoin/libblkmaker
+          path: libblkmaker
 
       - name: Create build directory
         run: mkdir -p build