pw_presubmit: Ignore copyright for docker/tag
pw_presubmit: Ignore copyright for docker/tag

Skip docker/tag when checking for copyright headers. This file will
contain the tag of the most recently built docker image.

Bug: 216
Change-Id: Ib706fa4d661f79b09fc3d2df9ae5f59bb0a107e1
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/15221
Reviewed-by: Keir Mierle <69344103cc60b36d6e1fbdc31ce6504b2286c646@google.com>
Commit-Queue: Rob Mohr <d07614a8a0b466db08f68224f87d738b0f9615cf@google.com>

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