Disable logging when tests are run

This should hopefully fix CI and running in containers that don't
have an active rsyslog daemon.

export/Makefile

@@ -16,7 +16,8 @@ check-black: ## Check Python source code formatting with black
 TESTS ?= tests
 .PHONY: test
 test:  ## Run tests
-	poetry run pytest -v --cov-report html --cov-report term-missing --cov=securedrop_export $$TESTS
+	poetry run pytest -v --cov-report html --cov-report term-missing \
+		--cov=securedrop_export --log-disable=securedrop_export.main $$TESTS
 
 .PHONY: lint
 lint:  ## Run linter