feat: Add location and begin_time fields to SponsoredEventListSerializer and update tests

[serkodev]

Types of changes

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• Bugfix
• New feature
• Refactoring
• Breaking change (any change that would cause existing functionality to not work as expected)
• Documentation Update
• Other (please describe)

Description

add missing response field in sponsor talks.

Steps to Test This Pull Request

Steps to reproduce the behavior:
request /events/speeches/?event_types=talk,sponsored

Expected behavior

talk and sponsor talk data struct same

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.80%. Comparing base (aed3685) to head (e5f24b5).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1273      +/-   ##
==========================================
+ Coverage   74.60%   78.80%   +4.19%     
==========================================
  Files          84       85       +1     
  Lines        3186     3250      +64     
==========================================
+ Hits         2377     2561     +184     
+ Misses        809      689     -120     

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[limouren]

I cannot reproduce but the changes look harmless. LGTM.

[limouren]

LGTM