chore(deps-dev): bump @ideal-postcodes/jsutil from 4.6.0 to 6.4.0

Bumps [@ideal-postcodes/jsutil](https://github.com/ideal-postcodes/jsutil) from 4.6.0 to 6.4.0.
- [Commits](https://github.com/ideal-postcodes/jsutil/commits)

---
updated-dependencies:
- dependency-name: "@ideal-postcodes/jsutil"
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

package.json

@@ -49,7 +49,7 @@
     "@cablanchard/tsconfig": "~2.0.0",
     "@ideal-postcodes/api-fixtures": "~1.2.0",
     "@ideal-postcodes/api-typings": "~2.1.0",
-    "@ideal-postcodes/jsutil": "~4.6.0",
+    "@ideal-postcodes/jsutil": "~6.4.0",
     "@prettier/plugin-php": "~0.18.4",
     "@prettier/plugin-xml": "~0.13.1",
     "@rollup/plugin-commonjs": "~21.0.2",