CI: install latest mesa drivers & xvfb directly

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

.github/workflows/ci.yml

@@ -25,14 +25,14 @@ jobs:
           AGREE: true
       - name: x86_64-linux -> x86_64-windows
         run: zig build test -Dtarget=x86_64-windows
-      - name: mach::test (xvfb)
-        uses: GabrielBB/xvfb-action@v1
-        with:
-          run: zig build test
-      - name: webgpu::test (xvfb)
-        uses: GabrielBB/xvfb-action@v1
-        with:
-          run: cd webgpu && zig build test
+      - name: mach::test
+        run: |
+          sudo add-apt-repository -y ppa:kisak/kisak-mesa
+          sudo apt-get update
+          sudo apt-get install mesa-utils mesa-utils-extra mesa-va-drivers mesa-vdpau-drivers mesa-vulkan-drivers xvfb
+          zig build test
+      - name: webgpu::test
+        run: cd webgpu && zig build test
   x86_64-windows:
     runs-on: windows-latest
     # We want to run on external PRs, but not on our own internal PRs as they'll be run by the push