ci: retry apt-get update and install to absorb transient mirror failures

.github/workflows/actions/use-nodes/action.yml

@@ -5,7 +5,26 @@ runs:
   steps:
     - name: Install dependencies
       shell: bash
-      run: sudo apt-get update && sudo apt-get install -y curl gcc make clang cmake
+      run: |
+        set -euo pipefail
+
+        apt_get() {
+          sudo apt-get -o Acquire::Retries=3 -o Acquire::http::Timeout=30 "$@"
+        }
+
+        attempts=3
+        for attempt in $(seq "$attempts"); do
+          if apt_get -o APT::Update::Error-Mode=any update && apt_get install -y curl gcc make clang cmake; then
+            exit 0
+          fi
+
+          if [ "$attempt" -lt "$attempts" ]; then
+            sleep $((attempt * 10))
+          fi
+        done
+
+        echo "::error::apt-get update/install failed after $attempts attempts"
+        exit 1
 
     - name: Download substrate-node binary
       id: download-substrate-binary

.github/workflows/build-nodes.yml

@@ -18,7 +18,26 @@ jobs:
           repository: paritytech/polkadot-sdk
 
       - name: Install dependencies
-        run: sudo apt-get update && sudo apt-get install -y protobuf-compiler curl gcc make clang cmake llvm-dev libclang-dev
+        run: |
+          set -euo pipefail
+
+          apt_get() {
+            sudo apt-get -o Acquire::Retries=3 -o Acquire::http::Timeout=30 "$@"
+          }
+
+          attempts=3
+          for attempt in $(seq "$attempts"); do
+            if apt_get -o APT::Update::Error-Mode=any update && apt_get install -y protobuf-compiler curl gcc make clang cmake llvm-dev libclang-dev; then
+              exit 0
+            fi
+
+            if [ "$attempt" -lt "$attempts" ]; then
+              sleep $((attempt * 10))
+            fi
+          done
+
+          echo "::error::apt-get update/install failed after $attempts attempts"
+          exit 1
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1