Adjust shader test CI workflows

.github/workflows/linux.yml

@@ -96,7 +96,7 @@ jobs:
       - name: Install deps
         run: |
           source ./util/ci/common.sh
-          install_linux_deps clang-11
+          install_linux_deps clang-11 xvfb
 
       - name: Build
         run: |
@@ -104,13 +104,17 @@ jobs:
         env:
           CC: clang-11
           CXX: clang++-11
-          # Test fallback SHA implementations
-          CMAKE_FLAGS: '-DENABLE_OPENSSL=0'
+          # Test fallback SHA implementations, add GLES for the test
+          CMAKE_FLAGS: '-DENABLE_OPENSSL=0 -DENABLE_GLES2=ON'
 
       - name: Test
         run: |
           ./bin/luanti --run-unittests
 
+      - name: Singleplayer test (GLES)
+        run: |
+          clientconf="video_driver=ogles2" xvfb-run ./util/test_singleplayer.sh
+
   # Current clang version
   clang_18:
     runs-on: ubuntu-24.04
@@ -136,9 +140,9 @@ jobs:
         run: |
           ./util/test_multiplayer.sh
 
-      - name: Singleplayer test
+      - name: Singleplayer test (GL3)
         run: |
-          xvfb-run ./util/test_singleplayer.sh
+          clientconf="video_driver=opengl3" xvfb-run ./util/test_singleplayer.sh
 
   # Build with prometheus-cpp (server-only), also runs on ARM64
   clang_prometheus_arm: