chore(nodejs): Add system-test/fixtures to .eslintignore (#720)

* fix: Add `system-test/fixtures` to `.eslintignore`

* refactor: Use `**`

Source-Link: googleapis/synthtool@b7858ba
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:abc68a9bbf4fa808b25fa16d3b11141059dc757dbc34f024744bba36c200b40f

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

handwritten/nodejs-logging-bunyan/.eslintignore

@@ -5,3 +5,4 @@ build/
 docs/
 protos/
 samples/generated/
+system-test/**/fixtures