fixes #4811

[rahulr-96]

New Pull Request

This PR addresses an inconsistency in the tooltip label behavior. Previously, on configuring tooltip for multiple y series, when a formatter function was provided only for the tooltip value, the title's default formatter applied differed from when no formatter was provided. Now, the title will maintain a consistent default format regardless of whether a value formatter is used alone.

Fixes #4811

Type of change

Please delete options that are not relevant.

• 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)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My branch is up to date with any changes from the main branch