Increase the timeout of ChannelDeregistrationTest

Motivation:

When a thread-local random is used first time, it tries to get the
initial seed uniquifier from SecureRandom, and it sometimes takes time
for the system to have enough entropy.

In ChannelDeregistrationTest, the retrieval of the initial seed
uniquifier takes place lazily when a new channel is created, and it
blocks the channel creation for more than 2 seconds, resulting in test
timeouts.

Modifications:

Increase the timeout of the tests to 5 seconds, because the timeout of
the initial seed uniquifier retrieval is 3 seconds.

Result:

Less flakey tests