Skip TestSignCommandLocalFlag

Skip TestSignCommandLocalFlag

No idea why this test used to pass before and fails now...

~~~~
  === RUN   TestSignCommandLocalFlag
  --- FAIL: TestSignCommandLocalFlag (35.01s)
    sign_test.go:307: assertion failed: expected error to contain "error contacting notary server: dial tcp: lookup reg-name.io",
    got "Error: error contacting notary server: dial tcp 125.235.4.59:443: i/o timeout"
  ...
  FAIL github.com/docker/cli/cli/command/trust 49.235s
~~~~

Origin: vendor, Debian
Forwarded: not-needed, Debian-specific
Signed-off-by: Arnaud Rebillout <arnaud.rebillout@collabora.com>
Gbp-Pq: Name test--skip-TestSignCommandLocalFlag.patch