Add an apt-get update step to the ubuntu CI builds.

This stops it from getting an HTTP 404 while downloading
dependencies if they have been updated since the image
came out. This has been an issue for example with the
check-docker-image build, which was failing because of
a dependency moved.

Author: NlightNFotis

.github/workflows/pull-request-checks.yaml

@@ -16,6 +16,7 @@ jobs:
           # user input
           DEBIAN_FRONTEND: noninteractive
         run: |
+          sudo apt-get update
           sudo apt-get install --no-install-recommends -yq gcc gdb g++ maven jq flex bison libxml2-utils ccache cmake
       - name: Prepare ccache
         uses: actions/cache@v2
@@ -70,6 +71,7 @@ jobs:
           # user input
           DEBIAN_FRONTEND: noninteractive
         run: |
+          sudo apt-get update
           sudo apt-get install --no-install-recommends -yq cmake ninja-build gcc g++ maven flex bison libxml2-utils dpkg-dev ccache doxygen
       - name: Prepare ccache
         uses: actions/cache@v2
@@ -232,6 +234,7 @@ jobs:
           # user input
           DEBIAN_FRONTEND: noninteractive
         run: |
+          sudo apt-get update
           sudo apt-get install --no-install-recommends -yq clang-format-7
       - name: Check updated lines of code match clang-format-7 style
         env:
@@ -313,7 +316,9 @@ jobs:
         with:
           submodules: recursive
       - name: Fetch dependencies
-        run: sudo apt-get install --no-install-recommends -y g++ flex bison cmake ninja-build maven jq libxml2-utils dpkg-dev ccache
+        run: | 
+          sudo apt-get update
+          sudo apt-get install --no-install-recommends -y g++ flex bison cmake ninja-build maven jq libxml2-utils dpkg-dev ccache
       - name: Prepare ccache
         uses: actions/cache@v2
         with:
@@ -365,7 +370,9 @@ jobs:
         with:
           submodules: recursive
       - name: Download test dependencies
-        run: sudo apt install openjdk-11-jdk-headless
+        run: |
+          sudo apt update
+          sudo apt install openjdk-11-jdk-headless
       - name: Build docker image
         run: docker build -t cbmc .
       - name: Smoke test goto-cc