The `gh cs ssh` command suggests an example recipe for setting up
openssh integration. The last step appends an `Include` statement to the
user's `~/.ssh/config`.
Unfortunately, this won't always work as intended. If the existing
configuration ends with a `Host` block, the added `Include` statement
will be conditional on whether that block matches.
By preceding the `Include` statement with `Match all`, we can ensure
that it is always evaluated.
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