Fix versioning filename examples

[lntutor]

Fixes #117.

Updates every VersioningXX.json reference in the versioning guide to the documented Versioning_XX.json filename template.

Validation:

• mkdocs build
• Verified no VersioningXX.json references remain in the guide
• git diff --check

mkdocs build --strict still reports the repository existing unresolved-link warnings; the regular CI-equivalent build completes successfully.