third_party/fuchsia: Replace list with typing.List
third_party/fuchsia: Replace list with typing.List

Use typing.List[] in place of list[] which is not supported by
Python 3.8.

Change-Id: Id3bd3dab788e78ceac19e50e46f2aeef49184248
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/111532
Pigweed-Auto-Submit: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

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