Drift: PMIx_App_string

List: https://github.com/openpmix/pmix-tests/blob/08705b12294fc5020f2af951b9bb10b36b6cec8d/check-standard/etc/openpmix_master-pmix-standard_master.txt#L185-L190

```
#---------------------------------------------------------
# Needs Review:
#  OpenPMIx: d56cc5fdb
#  OpenPMIx PR: 
#---------------------------------------------------------
PMIx_App_string
```