CI: Don't bother with main/linux-*/config-* in kconfig check (MR 5838)

We haven't had kernels in main/ for soon three years[1], so no need
to bother checking this location.

 [1]: See commits 47d8f823..8f24fe3a
[ci:skip-build]: already built successfully in CI

.gitlab-ci.yml

@@ -109,7 +109,6 @@ kernel-kconfig:
       changes:
         - kconfigcheck.toml
         - device/*/linux-*/config-*
-        - main/linux-*/config-*
   script:
     - .ci/lib/gitlab_prepare_ci.sh
     - .ci/kconfig.sh