Source Amplitude: fix most recent cursor value

[roman-yermilov-gl]

What

#25367

How

• Fix Event stream: use start_time instead of cursor in the case of more recent
• Shifted start_date to more recent value and updated expected records

[github-actions]

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[github-actions]

source-amplitude test report (commit bbe4fc166f) - ✅

⏲️ Total pipeline duration: 12mn37s

Step	Result
Connector package install	✅
Build source-amplitude docker image for platform linux/x86_64	✅
Unit tests	✅
Acceptance tests	✅
Code format checks	✅
Validate airbyte-integrations/connectors/source-amplitude/metadata.yaml	✅
Connector version semver check	✅
Connector version increment check	✅
QA checks	✅

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[lazebnyi]

please add comment how cursor look like for different conditions