chore(gitignore): ignore coverage.json pytest-cov export

.gitignore already covered .coverage (the SQLite raw-data file) and
htmlcov/ (the HTML export). Adding coverage.json — the JSON export
produced by pytest-cov --cov-report=json — closes a small gap where
that artifact would show up as untracked after every coverage run.

Author: RelativisticJet

.gitignore

@@ -23,6 +23,7 @@ __pycache__/
 .pytest_cache/
 .coverage
 htmlcov/
+coverage.json
 
 # Splunk local configuration (should not be committed)
 local/