regression 1.49: warn/deny annotations after forbid annotation breaks build

[rylev]

https://crater-reports.s3.amazonaws.com/beta-1.49-1/beta-2020-11-26/reg/zkp-criterion-utils-0.2.0/log.txt
https://crater-reports.s3.amazonaws.com/beta-1.49-1/beta-2020-11-26/reg/zkp-u256-0.2.0/log.txt
https://crater-reports.s3.amazonaws.com/beta-1.49-1/beta-2020-11-26/reg/as-dyn-trait-0.2.0/log.txt
https://crater-reports.s3.amazonaws.com/beta-1.49-1/beta-2020-11-26/reg/kmp-0.1.1/log.txt

[INFO] [stdout] error[E0453]: warn(unsafe_code) incompatible with previous forbid in same scope
[INFO] [stdout]   --> src/lib.rs:35:5
[INFO] [stdout]    |
[INFO] [stdout] 6  | #![forbid(unsafe_code)]
[INFO] [stdout]    |           ----------- `forbid` level set here
[INFO] [stdout] ...
[INFO] [stdout] 35 |     unsafe_code,
[INFO] [stdout]    |     ^^^^^^^^^^^

@rustbot modify labels: +regression-from-stable-to-beta

[rylev]

This was already reported in #77713 and is open to be reverted in #79903. Closing this as a duplicate.