fixup! CI: use apt.llvm.org directly

.github/workflows/linux.yaml

@@ -33,11 +33,42 @@ jobs:
 
       - name: Run tests
         run: ctest --test-dir _build
+
+  Linux-Clang-7:
+    runs-on: ubuntu-20.04
+    env:
+      CMAKE_OPTIONS: -DDEV_MODE=ON -DBUILD_TESTING=ON -G Ninja -DCMAKE_CXX_FLAGS="-stdlib=libc++"
+    steps:
+      - uses: lukka/get-cmake@latest
+
+      - name: Install libc++
+        run: |
+          wget -qO - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+          sudo add-apt-repository --yes --update deb http://apt.llvm.org/focal/ llvm-toolchain-focal-7 main
+          sudo apt-get update
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install -yq --no-install-recommends clang-7 llvm-7
+          sudo apt install -y libc++abi-7-dev libc++-7-dev
+
+      - name: Get pushed code
+        uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -S . -B _build ${{ env.CMAKE_OPTIONS }} -DCMAKE_INSTALL_PREFIX:STRING=${GITHUB_WORKSPACE}/_built
+
+      - name: Build
+        run: cmake --build _build --parallel
+
+      - name: Test installation
+        run: cmake --install _build --prefix ${GITHUB_WORKSPACE}/_built
+
+      - name: Run tests
+        run: ctest --test-dir _build
+
   Linux-Clang:
     runs-on: ubuntu-24.04
     strategy:
       matrix:
-        cxx: ['7', '19']
+        cxx: ['19']
     env:
       CMAKE_OPTIONS: -DDEV_MODE=ON -DBUILD_TESTING=ON -G Ninja -DCMAKE_CXX_FLAGS="-stdlib=libc++"
     steps:
@@ -48,6 +79,7 @@ jobs:
           wget -qO - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
           sudo add-apt-repository --yes --update deb http://apt.llvm.org/noble/ llvm-toolchain-noble-${{matrix.cxx}} main
           sudo apt-get update
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install -yq --no-install-recommends clang-${{matrix.cxx}} llvm-${{matrix.cxx}}
           sudo apt install -y libc++abi-${{matrix.cxx}}-dev libc++-${{matrix.cxx}}-dev
 
       - name: Get pushed code