gitlab-ci: Switch the meson-main build type to debugoptimized.

Now that we're running the drivers we build, building with
optimization is important for keeping our runtime down.  Shaves about
4 minutes of runtime off of GLES2 CTS of llvmpipe at 64x64.

v2: Only switch meson-main until we enable CTS for other builds
    on request by Michel.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9861f75..aca5d76 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -175,6 +175,7 @@
       -D osmesa=gallium
       -D tools=all
     MESON_SHADERDB: "true"
+    BUILDTYPE: "debugoptimized"
 
 meson-clover:
   extends: .meson-build