make Shard.in_current_region scope smarter
make Shard.in_current_region scope smarter

use an inverse condition to make the query shorter if possible

Change-Id: I1b1dbd31ca1a8e9b2355e2209f0932e22cd517a1
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/251593
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Ethan Vizitei <73eeb0b2f65d05a906adf3b21ee1f9f5a2aa3c1c@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

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