Also checkout release branch in upload release step

[mokagio]

When I worked on #1675 I decided not to checkout the release branch in the upload step because I thought "it's just downloading the artifact and sending it to ASC, we have it in a dedicated step just so if the upload fails we don't need to re-run the whole build process."

Alas, I had forgotten that step also uploads the dSYM to Sentry and creates the GitHub release. (The name upload_to_testflight doesn't help remembering it).

When the release is created, the automation reads the version from the codebase, meaning we need to be on the latest commit. Otherwise, we'll do like in the last build where we uploaded 4.55.0.2 to TestFlight but created a release named 4.55.0.1 (since then deleted)

[mokagio]

Bypassing CI checks because this change does not run in the standard CI pipeline. We'll validate it next by retrying the complete code freeze pipeline. Same as #1669, #1675, etc.

[dangermattic]

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	App Name	Simplenote Prototype Build
	Build Number	pr1677-16544b0-0192dedf-f092-4c10-b381-1ba1e51d6614
	Version	4.55
	Bundle ID	com.codality.NotationalFlow.Alpha
	Commit	16544b0
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