Add Github Actions CI for Ubuntu 20.20

Author: hannes-steffenhagen-diffblue

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

@@ -4,6 +4,28 @@ on:
     branches: [ develop ]
 
 jobs:
+  check-ubuntu-20_04-cmake-gcc:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          submodules: true
+      - name: Fetch dependencies
+        env:
+          # This is needed in addition to -yq to prevent apt-get from asking for
+          # user input
+          DEBIAN_FRONTEND: noninteractive
+        run: sudo apt-get install -yq cmake ninja-build gcc g++ maven flex bison
+      - name: Configure using CMake
+        run: |
+          mkdir build
+          cd build
+          cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_COMPILER=/usr/bin/gcc -DCMAKE_CXX_COMPILER=/usr/bin/g++
+      - name: Build with Ninja
+        run: cd build; ninja
+      - name: Run tests
+        run: cd build; ctest . -V -L CORE
+
   check-macos-10_15-cmake-clang:
     runs-on: macos-10.15
     steps: