CI: speed up gcc Ubuntu run

This is an attempt to speed up the gcc CI job on the Ubuntu runner, which
spends between 2 and 3 minutes on apt-get update and apt-get install.

Without apt-get update, the installation of the dependencies (ccache and z3)
now takes 20 seconds.

Author: kroening

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

@@ -18,11 +18,11 @@ jobs:
           # This is needed in addition to -yq to prevent apt-get from asking for
           # user input
           DEBIAN_FRONTEND: noninteractive
-        run: |
-          sudo apt-get update
-          sudo apt-get install --no-install-recommends -yq gcc gdb g++ jq flex bison libxml2-utils ccache cmake z3
+        run: sudo apt-get install --no-install-recommends -yq ccache z3
       - name: Confirm z3 solver is available and log the version installed
         run: z3 --version
+      - name: Log the version of gcc
+        run: gcc --version
       - name: Prepare ccache
         uses: actions/cache@v4
         with: