remove "ssh://" prefix from git repo value in gitsync instructions in helm docs

[wherrmann]

Documentation-only change.

Revises helm chart docs so that the Mange DAGs Files >> Mounting DAGs From a Private Github Repo Using GitSync Sidecar section advises the correct format for specifying the private git repo address.

closes: #21970

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[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[potiuk]

Thanks. Yeah. It was misleading.