build(deps): bump @material-ui/core from 4.12.3 to 4.12.4

Bumps [@material-ui/core](https://github.com/mui-org/material-ui/tree/HEAD/packages/material-ui) from 4.12.3 to 4.12.4.
- [Release notes](https://github.com/mui-org/material-ui/releases)
- [Changelog](https://github.com/mui/material-ui/blob/v4.12.4/CHANGELOG.md)
- [Commits](https://github.com/mui-org/material-ui/commits/v4.12.4/packages/material-ui)

---
updated-dependencies:
- dependency-name: "@material-ui/core"
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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