Fix mock in unit test after removing deprecated snowplow method

[mikealfare]

Problem

We removed a deprecated method, snowplow_tracker.Tracker.track_struct_event(), and replaced it with the suggested method snowplow_tracker.Tracker.track(). The former was mocked in a unit test and it was expected to be called. After the update, it did not get called as this method no longer existed.

Solution

Update the mock to reference the new method.

Checklist

• I have read the contributing guide and understand what's expected of me.
• I have run this code in development, and it appears to resolve the stated issue.
• This PR includes tests, or tests are not required or relevant for this PR.
• This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• This PR includes type annotations for new and modified functions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.96%. Comparing base (3e437a6) to head (a9e947d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10738      +/-   ##
==========================================
+ Coverage   86.12%   88.96%   +2.83%     
==========================================
  Files         181      181              
  Lines       22964    22964              
==========================================
+ Hits        19777    20429     +652     
+ Misses       3187     2535     -652     

Flag	Coverage Δ
integration	86.13% <ø> (+0.01%)	⬆️
unit	62.40% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Unit Tests	62.40% <ø> (∅)
Integration Tests	86.13% <ø> (+0.01%)	⬆️