zeek: Ignore some paths in the coverage output (google#9669)

I was only able to test these paths by passing them as arguments to
`infra/helper.py` but not built-in to the image itself locally. I'm not
sure if that's intentional, but passing them as arguments did what I
wanted it to do.

projects/zeek/project.yaml

@@ -17,3 +17,7 @@ fuzzing_engines:
 sanitizers:
   - address
 main_repo: 'https://github.com/zeek/zeek'
+coverage_extra_args: >
+  -ignore-filename-regex=src/3rdparty/.*
+  -ignore-filename-regex=build/zeek/3rdparty/.*
+  -ignore-filename-regex=auxil/.*