Try to use the Clang packages instead.

Change-Id: Ic92c59dccfd27bc470dd4d78cf383739c7b96383
Reviewed-on: https://code-review.googlesource.com/c/re2/+/57802
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8a892b2..e81dd36 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,16 +17,19 @@
       shell: bash
   build-clang:
     runs-on: ubuntu-latest
-    container: ericwf/llvm:${{ matrix.tag }}
     strategy:
       matrix:
-        tag: [4.x, 5.x, 6.x, 7.x, 8.x, 9.x, 10.x, 11.x]
+        tag: [9, 10, 11]
     env:
-      CC: /compiler/bin/clang
-      CXX: /compiler/bin/clang++
+      CC: clang-${{ matrix.tag }}
+      CXX: clang++-${{ matrix.tag }}
     steps:
     - uses: actions/checkout@v2
-    - run: apt update && apt install make
+    - name: Install Clang ${{ matrix.tag }}
+      run: |
+        wget https://apt.llvm.org/llvm.sh
+        chmod +x ./llvm.sh
+        sudo ./llvm.sh ${{ matrix.tag }}
       shell: bash
     - run: make && make test
       shell: bash