lib/promscrape/discovery/kubernetes: supress context.Cancelled error in logs
It is possible that context.Cancelled will appear after k8s watcher was closed due to reload(see https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4850).
Logging an error misinforms user and looks like vmagent discovery will stop working even though this does not affect discovery.
Signed-off-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>
(cherry picked from commit 8d99c12a7d)
0be8960875