pw_unit_test: Fixup documentation
pw_unit_test: Fixup documentation

* Fix typos in the unit test documentation

Change-Id: I7dec4c8228a487e0dc3562abdc214d612688a635
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/44440
Reviewed-by: Keir Mierle <69344103cc60b36d6e1fbdc31ce6504b2286c646@google.com>
Reviewed-by: Armando Montanez <97ef6fdb231c129ac8827d9f0c4106bfbf57f74f@google.com>
Commit-Queue: Keir Mierle <69344103cc60b36d6e1fbdc31ce6504b2286c646@google.com>

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