Fix TRANSCODING_SEPARATOR import errors

[ravi-kumar-pilla]

Description

Resolves #1865

Development notes

With the PR - https://github.com/kedro-org/kedro/pull/3812/files TRANSCODING_SEPARATOR has been moved from kedro/pipeline/pipeline.py to kedro/pipeline/_transcoding.py. Since kedro-viz imports these, we need to handle the import error before the latest kedro release.

QA notes

• All tests should pass

Checklist

• [x] Read the contributing guidelines
• [ ] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [ ] Updated the documentation to reflect the code changes
• [x] Added new entries to the RELEASE.md file
• [ ] Added tests to cover my changes