Print stderrs in tools/mypy_wrapper.py (#58265)
Summary:
Uncovered while investigating https://github.com/pytorch/pytorch/issues/58253.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58265
Test Plan:
Before this PR:
```
$ mypy tools/stats_utils/foo.txt
mypy: can't read file 'tools/stats_utils/foo.txt': No such file or directory
$ echo $?
2
$ tools/mypy_wrapper.py $PWD/tools/stats_utils/foo.txt
$ echo $?
2
```
After this PR:
```
$ mypy tools/stats_utils/foo.txt
mypy: can't read file 'tools/stats_utils/foo.txt': No such file or directory
$ echo $?
2
$ tools/mypy_wrapper.py $PWD/tools/stats_utils/foo.txt > /dev/null
mypy: can't read file 'tools/stats_utils/foo.txt': No such file or directory
mypy: can't read file 'tools/stats_utils/foo.txt': No such file or directory
$ echo $?
2
```
Reviewed By: zhouzhuojie
Differential Revision: D28426439
Pulled By: samestep
fbshipit-source-id: c47a85a696ed44c9873416decc9fed8d99bc556c
