switch transient attachment error in jobs to Delayed::RetriableError
switch transient attachment error in jobs to Delayed::RetriableError

refs INTEROP-6674

test plan: see cec0fc7b067694623ca4195749484f2e1707e8d3, but no error
should be logged

Change-Id: If7b74e69bb293bd99f3166bff1354f4b4cdaab5f
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/263806
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Keith Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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