[Fix] (CI): name the EGL vendor library the benchmark job runs on

The benchmark job is the only one that brings a real GL context up - DriverBench
dlopens libEGL.so.1 and renders through it - but its apt list only asks for
libegl1, which is glvnd's dispatch layer and nothing more. The vendor library
behind it, libegl-mesa0, has been arriving as a Recommends of libegl1 rather
than because anything asked for it. That is too quiet a dependency for the one
job whose whole purpose is running a driver: a base image change, or
--no-install-recommends turning up anywhere upstream, would leave eglInitialize
with no vendor to dispatch to and fail the job for a reason nothing in the
workflow explains. Name it, next to libgl1-mesa-dri, which is listed for
exactly the same reason.

Verified with a full headless ctest -C Release -L benchmark - no $DISPLAY, no
$EGL_PLATFORM, mesa as the only EGL vendor: SanityBench, ProgramBench,
BufferBench and DriverBench all pass.

.github/workflows/test.yml

@@ -177,9 +177,13 @@ jobs:
         uses: lukka/get-cmake@v4.3.3
 
       - name: Install runtime dependencies
+        # libegl-mesa0 is the EGL vendor library itself: DriverBench brings up a
+        # real GL context, and libegl1 is only glvnd's dispatch. It normally
+        # arrives as a Recommends of libegl1, which is too quiet a dependency for
+        # the one job that needs a working driver.
         run: |
           sudo apt-get update
-          sudo apt-get install -y libvulkan1 libegl1 libgles2 libgl1-mesa-dri mesa-vulkan-drivers
+          sudo apt-get install -y libvulkan1 libegl1 libegl-mesa0 libgles2 libgl1-mesa-dri mesa-vulkan-drivers
 
       - name: Download Linux runtime
         uses: actions/download-artifact@v8