[develop] Fix the inline-post issue when WRITE_DOPOST is 'true'

[chan-hoo]

DESCRIPTION OF CHANGES:

• Add the 'itag' namelist file for inline-post to 'run_dir' in the 'exregional_run_fcst' script.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

TESTS CONDUCTED:

• WE2E tests:
  inline_post
  nco_inline_post
  grid_RRFS_CONUS_25km_ics_FV3GFS_lbcs_FV3GFS_suite_GFS_v16

• hera.intel

• orion.intel

• cheyenne.intel

• cheyenne.gnu

• gaea.intel

• jet.intel

• wcoss2.intel

• NOAA Cloud (indicate which platform)

• Jenkins

• fundamental test suite

• comprehensive tests (specify which if a subset was used)

ISSUE:

Fixes issue mentioned in #371

CHECKLIST

• My code follows the style guidelines in the Contributor's Guide
• I have performed a self-review of my own code using the Code Reviewer's Guide
• I have commented my code, particularly in hard-to-understand areas
• My changes need updates to the documentation. I have made corresponding changes to the documentation
• My changes do not require updates to the documentation (explain).
• My changes generate no new warnings
• New and existing tests pass with my changes
• Any dependent changes have been merged and published

[danielabdi-noaa]

Looks like a critical bug fix so approving.