chore: bump LT release version related to snapshots

[mdevolde]

chore: bump LT release version related to snapshots

Why the pull request was made

A new tag is available on LanguageTool repo (6.8). So, snapshots versions are now related to future 6.9 version.
Bumping it in our repo allows users to download automatically the latest version in their env.

Summary of changes

• Bumped the LT_SNAPSHOT_CURRENT_VERSION and some references in the REAMDE.md.

Screenshots (if appropriate):

Not applicable.

How has this been tested?

Applied tests.

Resources

Not applicable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update (changes to documentation only)
• Refactor / code style update (non-breaking change that improves code structure or readability)
• Tests / CI improvement (adding or updating tests or CI configuration only)
• Other (please describe): chore update

Checklist

• Followed the project's contributing guidelines.
• Updated any relevant tests.
• Updated any relevant documentation.
• Added comments to your code where necessary.
• Formatted your code, run the linters, checked types and tests.