Bring azure-devtools's GH tool dependencies over to azure-sdk-tools

[mccoyp]

Description

After we fully removed azure-devtools from the SDK, @msyyc found that the SDK generation pipeline was now missing a GitPython dependency: #34956.

GitPython and PyGithub were previously being installed via azure-devtools/dev_requirements.txt or update-pr.yml. To fetch them correctly again, we need to add the former [ci_tools] dependencies to [ghtools] in azure-sdk-tools and correctly target [ghtools] from azure-sdk-tools/dev_requirements.txt.

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