automation/gitlab: disable coverage from clang randconfig

If randconfig enables coverage support the build times out due to GNU LD
taking too long.  For the time being prevent coverage from being enabled in
clang randconfig job.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Release-Acked-by: Oleksii Kurochko<oleksii.kurochko@gmail.com>

automation/gitlab-ci/build.yaml

@@ -556,6 +556,8 @@ debian-12-x86_64-clang-randconfig:
   variables:
     CONTAINER: debian:12-x86_64
     RANDCONFIG: y
+    EXTRA_FIXED_RANDCONFIG: |
+      CONFIG_COVERAGE=n # Disable coverage otherwise build times out.
 
 debian-12-x86_64-gcc:
   extends: .gcc-x86-64-build