servo: Merge #6279 - Add flake8 to the tidy process for Python files (from frewsxcv:flake8); r=jdm

Fixes #6236

Also included in this commit are the changes need to make flake8 pass
for the existing python file

Source-Repo: https://github.com/servo/servo
Source-Revision: ccfe29d8f284dedc0101045d574a98fb1f69aa62

servo/python/licenseck.py

@@ -59,4 +59,4 @@ licenses = [
 # except according to those terms.
 """,
 
-]
+]  # noqa: Indicate to flake8 that we do not want to check indentation here