fixup! CI: add a target with older Ubuntu to test older compilers

Author: robUx4

.github/workflows/ubuntu-20.04.yaml

@@ -6,56 +6,28 @@ on:
     # branches: [ master ]
 
 jobs:
-  GCC-7:
+  Oldest:
     runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        compiler: [
+          { "name": "gcc",   "version": "7", "cpp": "g++"},
+          { "name": "clang", "version": "7", "cpp": "clang++"},
+        ]
     env:
       CMAKE_OPTIONS: -DDEV_MODE=ON -DBUILD_TESTING=ON
       CMAKE_MATROSKA_OPTIONS: -DBUILD_EXAMPLES=ON
+      CXX: ${{ matrix.compiler.cpp }}-${{ matrix.compiler.version }}
     steps:
-      - uses: egor-tensin/setup-gcc@v1
-        with:
-          version: 7
-
-      - name: list compilers
-        run: dpkg --list | grep compiler
-
-      - name: Get pushed code
-        uses: actions/checkout@v4
-
-      - name: Checkout libebml
-        uses: actions/checkout@v4
-        with:
-          repository: Matroska-Org/libebml
-          path: libebml
-          # minimum version we support ref: 'release-1.4.3'
-
-      - name: Configure libebml
-        run: cmake -S libebml -B libebml/_build ${{ env.CMAKE_OPTIONS }}
-
-      - name: Build libebml
-        run: cmake --build libebml/_build --parallel
-
-      - name: Install libebml
-        run: cmake --install libebml/_build --prefix ${GITHUB_WORKSPACE}/_built
-
-      - name: Configure
-        run: cmake -S . -B _build  ${{ env.CMAKE_OPTIONS }} ${{ env.CMAKE_MATROSKA_OPTIONS }} -DEBML_DIR="${GITHUB_WORKSPACE}/_built/lib/cmake/EBML"
-
-      - name: Build
-        run: cmake --build _build --parallel
-
-      - name: Test installation
-        run: cmake --install _build --prefix ${GITHUB_WORKSPACE}/_built
-
-  Clang-7:
-    runs-on: ubuntu-20.04
-    env:
-      CMAKE_OPTIONS: -DDEV_MODE=ON -DBUILD_TESTING=ON
-      CMAKE_MATROSKA_OPTIONS: -DBUILD_EXAMPLES=ON
-    steps:
-      - uses: egor-tensin/setup-clang@v1
-        with:
-          version: 7
+      # - uses: egor-tensin/setup-gcc@v1
+      #   with:
+      #     version: 7
+
+      - name: Install
+        # we need the apt update because old packages won't load
+        run: |
+          sudo apt update
+          sudo apt install ${{ matrix.compiler.cpp }}-${{ matrix.compiler.version }}
 
       - name: list compilers
         run: dpkg --list | grep compiler