docs(eval): fix 'Coverts' typo in RubricBasedToolUseV1Evaluator docstring

[anxkhn]

Please ensure you have read the contribution guide before creating a pull request.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• N/A (small typo fix; per CONTRIBUTING, documentation/typo fixes do not require an associated issue)

2. Or, if no issue exists, describe the change:

Problem:
The class docstring of RubricBasedToolUseV1Evaluator in
src/google/adk/evaluation/rubric_based_tool_use_quality_v1.py has a typo in its
worked example: "GeoCoding Tool: Coverts a city name, address or zip code into
geographic coordinates." "Coverts" should be "Converts".

Solution:
Fix the single-word typo Coverts -> Converts. Documentation-only change, no
behavior change.

-  1: GeoCoding Tool: Coverts a city name, address or zip code into geographic
+  1: GeoCoding Tool: Converts a city name, address or zip code into geographic
   coordinates.

Testing Plan

This is a small documentation/typo fix (no code behavior change), which the PR
template notes does not require a testing plan. For completeness, I still ran the
evaluator's existing unit suite and it passes.

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

$ pytest tests/unittests/evaluation/test_rubric_based_tool_use_quality_v1.py -q
...                                                                      [100%]
3 passed

Manual End-to-End (E2E) Tests:

N/A. Documentation-only change; no runtime behavior is affected.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• 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.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

The adjacent line ("...into geographic coordinates.") was already corrected upstream
by PR #3382 ("chore: Fix spelling in src"), which fixed "cordinates" on the next
line but did not catch "Coverts". This PR closes that remaining gap.