gitlab-ci: Enable more Gallium drivers in meson-i386 job

These are the ones which can be enabled with the current x86_build
docker image and which build without warnings.

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4166>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4166>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index c89b5cd..66ba660 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -476,7 +476,7 @@
   variables:
     CROSS: i386
     VULKAN_DRIVERS: intel,amd
-    GALLIUM_DRIVERS: "iris"
+    GALLIUM_DRIVERS: "iris,r300,radeonsi,swrast,virgl"
     EXTRA_OPTION: >
       -D vulkan-overlay-layer=true
       -D werror=true