Refine the method defining destination path for aerosol obs

[RussTreadon-NOAA]

Description

This PR modifies a single line in ush/python/pygfs/task/aero_prepobs.py so that modification of the destination path for aerosol observation is limited to the basename part of the path.

This change is required to successfully run gcdas_prepobsaero from GDASApp ctest test_gdasapp_C96_gcafs_cycled

Resolves #3794

Type of change

• Bug fix (fixes something broken when running GDASApp ctests)

Change characteristics

• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? NO
• Does this change require an update to any of the following submodules? NO

How has this been tested?

Clone and build on Hera as part of GDASApp stable-nightly testing.

Checklist

• Any dependent changes have been merged and published
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added

[RussTreadon-NOAA]

This PR is required in order to successfully run GDASApp GCAFS ctests.

[CoryMartin-NOAA]

Thanks @RussTreadon-NOAA

[RussTreadon-NOAA]

Thank you @CoryMartin-NOAA for the quick review and approval.

test_gdasapp_C96_gcafs_cycled_gcdas_prepobsaero_202112201800 failed in GDASApp PR #1750 hera-GW-RT with

OSError: Unable to copy /scratch1/NCEPDEV/global/glopara/dump/gdas.20211220/18/atmos/gdas.t18z.viirs_npp_aod.tm00.nc to /scratch1/NCEPDEV/da/role.jedipara/CI/GDASApp/workflow/PR/1750/global-workflow/sorc/gcdas.cd/build/gcdas/test/gw-ci/../../test/gw-ci/C96_gcafs_cycled/COMROOT/C96_gcafs_cycled/gcdas.20211220/18/obs/gcdas.t18z.viirs_npp_aod.tm00.nc

This reminded me that we need this fix so that the path is /C96_gcafs_cycled/gdas.20211220/18/obs and not /C96_gcafs_cycled/gcdas.20211220/18/obs.

[RussTreadon-NOAA]

Thank you @aerorahul for the quick merge. Much appreciated!