Source S3: StreamReader and Cursor fixes

[Catherine Noll (clnoll)]

Fixes a couple of issues identified during end-to-end testing of the state message conversion:

• _running_migration and _v3_migration_start_datetime were not guaranteed to be set on the S3 cursor so I gave them default values on __init__. Alexandre Girard (@girarda) does it surprise you at all that they weren't set before being accessed?
• boto3 returns timezone-aware timestamps, but we need them to be timezone-naive, so I cast to UTC then strip the timezone from the LastModified timestamp.
• A cursor fix that wasn't affecting any tests but was inaccurate.

[github-actions]

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[Alexandre Girard (girarda)]

re: am I surprised they were accessed before being set?
A little bit, but in hindsight, it makes sense since set_initial_state isn't called on full refresh runs

[Alexandre Girard (girarda)]

Q: do you know if this was only a problem for full refresh?

either way, the fix looks good

[Catherine Noll (clnoll)]

It was happening in incremental syncs, too, but during the first run (before there is a state).

[Alexandre Girard (girarda)]

the 3 changes make sense to me. thanks for fixing!

[Octavia Squidington III (octavia-squidington-iii)]

source-s3 test report (commit d3b164d896) - ❌

⏲️ Total pipeline duration: 13mn33s

Step	Result
Validate airbyte-integrations/connectors/source-s3/metadata.yaml	✅
Connector version semver check	❌
Connector version increment check	❌
QA checks	✅
Code format checks	✅
Connector package install	✅
Build source-s3 docker image for platform linux/x86_64	✅
Unit tests	✅
Integration tests	✅
Acceptance tests	✅

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airbyte-ci connectors --name=source-s3 test

[Octavia Squidington III (octavia-squidington-iii)]

source-s3 test report (commit 7dc7b3b458) - ✅

⏲️ Total pipeline duration: 13mn40s

Step	Result
Validate airbyte-integrations/connectors/source-s3/metadata.yaml	✅
Connector version semver check	✅
Connector version increment check	✅
QA checks	✅
Code format checks	✅
Connector package install	✅
Build source-s3 docker image for platform linux/x86_64	✅
Unit tests	✅
Integration tests	✅
Acceptance tests	✅

🔗 View the logs here

☁️ View runs for commit in Dagger Cloud

Please note that tests are only run on PR ready for review. Please set your PR to draft mode to not flood the CI engine and upstream service on following commits.
You can run the same pipeline locally on this branch with the airbyte-ci tool with the following command

airbyte-ci connectors --name=source-s3 test