run apt-get update before fetching Ubuntu packages

.github/workflows/dynamic_arch.yml

@@ -42,6 +42,7 @@ jobs:
       - name: Install Dependencies
         run: |
           if [ "$RUNNER_OS" == "Linux" ]; then
+            sudo apt-get update
             sudo apt-get install -y gfortran cmake ccache libtinfo5
           elif [ "$RUNNER_OS" == "macOS" ]; then
             # It looks like "gfortran" isn't working correctly unless "gcc" is re-installed.