[DEPS]: Bump backstopjs from 6.1.1 to 6.1.3 in /tests/visual-regression

Bumps [backstopjs](https://github.com/garris/backstopjs) from 6.1.1 to 6.1.3.
- [Release notes](https://github.com/garris/backstopjs/releases)
- [Changelog](https://github.com/garris/BackstopJS/blob/master/changelog.md)
- [Commits](https://github.com/garris/backstopjs/commits/v6.1.3)

---
updated-dependencies:
- dependency-name: backstopjs
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

tests/visual-regression/package.json

@@ -9,7 +9,7 @@
     "author": "",
     "license": "GPL-2.0-or-later",
     "dependencies": {
-        "backstopjs": "^6.1.1"
+        "backstopjs": "^6.1.3"
     },
     "overrides": {
         "backstopjs": {