ci: Enable -Werror on meson-vulkan and meson-testing.

I want to make sure that I don't introduce warnings in turnip where we
have active work going on, and I also want to make sure that the drivers
we care about testing are warnings-clean.

As with the previous -Werror change, this is for CI only and doesn't
affect end-user builds.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3607>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3607>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index e83d68b..94fa883 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -261,6 +261,8 @@
     GALLIUM_DRIVERS: "swrast"
     VULKAN_DRIVERS: amd
     BUILDTYPE: "debugoptimized"
+    EXTRA_OPTION: >
+      -D werror=true
   script:
     - .gitlab-ci/meson-build.sh
     - .gitlab-ci/prepare-artifacts.sh
@@ -461,6 +463,7 @@
     VULKAN_DRIVERS: intel,amd,freedreno
     EXTRA_OPTION: >
       -D vulkan-overlay-layer=true
+      -D werror=true
 
 # While the main point of this build is testing the i386 cross build,
 # we also use this one to test some other options that are exclusive