Bump rocm-docs-core from 1.21.0 to 1.21.1 in /docs/sphinx

Bumps [rocm-docs-core](https://github.com/ROCm/rocm-docs-core) from 1.21.0 to 1.21.1.
- [Release notes](https://github.com/ROCm/rocm-docs-core/releases)
- [Changelog](https://github.com/ROCm/rocm-docs-core/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/ROCm/rocm-docs-core/compare/v1.21.0...v1.21.1)

---
updated-dependencies:
- dependency-name: rocm-docs-core
  dependency-version: 1.21.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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