Cast nodegroupid to string for check w/ serialized graph

[x] Bugfix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Closes archesproject/arches-her#1343

I targeted one of these branches:
- [ ] dev/7.6.x (under development): features, bugfixes not covered below
- [ ] dev/7.5.x (main support): regressions, crashing bugs, security issues, major bugs in new features
- [ ] dev/6.2.x (extended support): major security issues, data loss issues
[ ] I added a changelog in arches/releases
[ ] I submitted a PR to arches-docs (if appropriate)
[ ] Unit tests pass locally with my changes
[ ] I added tests that prove my fix is effective or that my feature works
[ ] My test fails on the target branch

archesproject / arches