pw_transfer: Fix integration test CLI arguments
pw_transfer: Fix integration test CLI arguments

Arguments like --server-port are used to override fields of the
TestHarness.Config, so these fields must be mutable. But NamedTuples,
like regular tuples, are immutable.

Tested: Locally, via
bazel run \
  pw_transfer/integration_test:cross_language_small_test -- \
  --server-port 3342

Change-Id: Id4243fe489e1500fa347ff4e47ef7ceedbbbf25d
Bug: 234875234
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/114790
Reviewed-by: Erik Gilling <1100d3bbb092e6691a138903fe8ea324306d03ea@google.com>
Commit-Queue: Ted Pudlik <c7372cc3e451acc046049fca9e050bcb2a4a3d11@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed