[github-actions] switch to using llvm install script (openthread#10837)

.github/workflows/build.yml

@@ -316,7 +316,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        clang_ver: ["9", "10", "11", "12", "13"]
+        clang_ver: ["17", "18", "19"]
     env:
       CC: clang-${{ matrix.clang_ver }}
       CXX: clang++-${{ matrix.clang_ver }}
@@ -331,15 +331,11 @@ jobs:
           submodules: true
       - name: Bootstrap
         run: |
-          sudo rm /etc/apt/sources.list.d/*
-          wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
-          echo 'deb http://apt.llvm.org/focal/ llvm-toolchain-focal main
-          deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal main
-          # 13
-          deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main
-          deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main' | sudo tee -a /etc/apt/sources.list
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh ${{ matrix.clang_ver }}
           sudo apt-get update
-          sudo apt-get --no-install-recommends install -y clang-${{ matrix.clang_ver }} clang++-${{ matrix.clang_ver }} ninja-build libreadline-dev libncurses-dev
+          sudo apt-get --no-install-recommends install -y ninja-build libreadline-dev libncurses-dev
       - name: Build
         run: |
           script/check-simulation-build