gitlab-ci: try to make the RPM build less noisy.

See whether unsetting VERBOSE causes the build process not to print the
compile command, complete with a big list of compiler options, for every
single file being built, in the hopes of producing less than the limit
of 4MB of log text.

.gitlab-ci.yml

@@ -162,6 +162,9 @@ build:rpm-fedora:
   extends: .build-rpm
   image: wireshark/wireshark-fedora-dev
   script:
+    # Shared GitLab runners limit the log size to 4M, so reduce verbosity. See
+    # https://gitlab.com/gitlab-com/support-forum/issues/2790
+    - unset VERBOSE
     - cmake3 -GNinja ..
     - ninja rpm-package
   needs: