Bump rocm-docs-core from 0.20.0 to 0.21.0 in /docs/.sphinx (ROCm#225)

Bumps [rocm-docs-core](https://github.com/RadeonOpenCompute/rocm-docs-core) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/RadeonOpenCompute/rocm-docs-core/releases)
- [Changelog](https://github.com/RadeonOpenCompute/rocm-docs-core/blob/develop/CHANGELOG.md)
- [Commits](ROCm/rocm-docs-core@v0.20.0...v0.21.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/.sphinx/requirements.in

@@ -1 +1 @@
-rocm-docs-core==0.20.0
+rocm-docs-core==0.21.0

docs/.sphinx/requirements.txt

@@ -92,7 +92,7 @@ requests==2.28.2
     # via
     #   pygithub
     #   sphinx
-rocm-docs-core==0.20.0
+rocm-docs-core==0.21.0
     # via -r requirements.in
 smmap==5.0.0
     # via gitdb