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 <keir@google.com>
Commit-Queue: Rob Mohr <mohrr@google.com>
diff --git a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
index eb37b7c..6f604fe 100755
--- a/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
+++ b/pw_presubmit/py/pw_presubmit/pigweed_presubmit.py
@@ -189,6 +189,7 @@
 
 _EXCLUDE_FROM_COPYRIGHT_NOTICE: Sequence[str] = (
     r'^(?:.+/)?\..+$',
+    r'^docker/tag$',
     r'\bAUTHORS$',
     r'\bLICENSE$',
     r'\bOWNERS$',