tests/functional: Drop the "Attempting to cache ..." log text

tests/functional: Drop the "Attempting to cache ..." log text

The fetch() function already either prints "Using cached asset ..."
or "Downloading ... to ..." with the same file name to the log,
so the "Attempting to cache ..." message does not provide any
additional valuable information. Thus let's drop it to limit the
length of the logging output to a more reasonable size.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20251006170304.197387-1-thuth@redhat.com>