pw_presubmit: Ignore dirs for banned words check

Bug: 386
Change-Id: I0df336feb01efb2d1fc03b11f0f828092491a5d4
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/46362
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Joe Ethier <jethier@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>

pw_presubmit/py/pw_presubmit/banned_words.py

diff --git a/pw_presubmit/py/pw_presubmit/banned_words.py b/pw_presubmit/py/pw_presubmit/banned_words.py
index f0812ac..8c789e6 100644
--- a/pw_presubmit/py/pw_presubmit/banned_words.py
+++ b/pw_presubmit/py/pw_presubmit/banned_words.py
@@ -115,7 +115,7 @@
                     # Not using 'continue' so this line always executes.
                     prev = line
 
-        except UnicodeDecodeError:
+        except (UnicodeDecodeError, IsADirectoryError):
             # File is not text, like a gif.
             pass