chore: [DevOps] bump the plugins group with 2 updates (#525)

Bumps the plugins group with 2 updates: [com.sap.cloud.sdk:sdk-bom](https://github.com/SAP/cloud-sdk-java) and [com.sap.cloud.sdk.datamodel:openapi-generator-maven-plugin](https://github.com/SAP/cloud-sdk-java).


Updates `com.sap.cloud.sdk:sdk-bom` from 5.20.0 to 5.21.0
- [Release notes](https://github.com/SAP/cloud-sdk-java/releases)
- [Changelog](https://github.com/SAP/cloud-sdk-java/blob/main/release_notes.md)
- [Commits](SAP/cloud-sdk-java@rel/5.20.0...rel/5.21.0)

Updates `com.sap.cloud.sdk.datamodel:openapi-generator-maven-plugin` from 5.20.0 to 5.21.0
- [Release notes](https://github.com/SAP/cloud-sdk-java/releases)
- [Changelog](https://github.com/SAP/cloud-sdk-java/blob/main/release_notes.md)
- [Commits](SAP/cloud-sdk-java@rel/5.20.0...rel/5.21.0)

---
updated-dependencies:
- dependency-name: com.sap.cloud.sdk:sdk-bom
  dependency-version: 5.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: plugins
- dependency-name: com.sap.cloud.sdk.datamodel:openapi-generator-maven-plugin
  dependency-version: 5.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: plugins
...

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

Author: dependabot[bot]