Fix backport bot flow (#16609)
Fix backport bot flow (#16609)

The backport portion of the review bot assumes its current working directory is a checkout
of teleport's master branch (see https://github.com/gravitational/shared-workflows/blob/main/bot/internal/bot/backport.go#L178)

And since `go run` needs the cwd to be right, switching to go build && exec instead

Deprecates #16608
gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport