fix alerts XSS vulnerability, fixes CNVS-17661

prevent XSS in the alerts UI by way of maliciously named account roles
(or less likely, malicious translations)

test plan: infer from comment above, or see ticket

Change-Id: Ia09a6535f238d2675bc9fb6d5aa93995ca4f2e5f
Reviewed-on: https://gerrit.instructure.com/46292
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>