Source GitHub: migrate repo and branches to array in spec

[artem1205]

What

Resolving #29744

How

change type of fields in spec:

1. repository : str -> array
2. branch: str -> array

⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇⬇

Recommended reading order

1. config_migrations.py
2. source.py

🚨 User Impact 🚨

no breaking changes

Pre-merge Actions

Updating a connector

Community member or Airbyter

• Grant edit access to maintainers (instructions)
• Unit & integration tests added

Airbyter

If this is a community PR, the Airbyte engineer reviewing this PR is responsible for the below items.

• Create a non-forked branch based on this PR and test the below items on it
• Build is successful
• If new credentials are required for use in CI, add them to GSM. Instructions.

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[github-actions]

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[airbyte-oss-build-runner]

source-github test report (commit dc89a077ad) - ✅

⏲️ Total pipeline duration: 03mn33s

Step	Result
Connector package install	✅
Build source-github docker image for platform(s) linux/x86_64	✅
Unit tests	✅
Acceptance tests	✅
Code format checks	✅
Validate metadata for source-github	✅
Connector version semver check	✅
Connector version increment check	✅
QA checks	✅

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