ci: avoid running the signed-off-by check in the schedule

The schedule only gives access to the latest commit via `--depth=1` and
that always is a merge commit. It isn't ignored by the `--no-merges`
option, because there only is one commit. Thus disable the check if it
is running as a schedule.

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

.github/workflows/ci.yml

@@ -206,6 +206,7 @@ jobs:
         env:
           RUSTFLAGS: "-Dwarnings"
   signed-off-by:
+    if: github.event_name != 'schedule'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4