[analyzer] Fix buildbots after introducing a new frontend warning

It seems like I should have ran the `check-clang` target after introducing a new warning diagnostic entry.
My bad. I'll run it next time; `check-clang-analysis` was not enough.
Here is a link to the broken bot: http://45.33.8.238/linux/78236/step_7.txt

This commit should fix this.

Differential Revision: https://reviews.llvm.org/D126067