gitlab: avoid extra pipelines for tags and stable branches

gitlab: avoid extra pipelines for tags and stable branches

In upstream context we only run pipelines on staging branches, and
limited publishing jobs on the default branch.

We don't want to run pipelines on stable branches, or tags, because
the content will have already been tested on a staging branch before
getting pushed.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230608164018.2520330-5-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>