Fix range size check if statements in diag_manager.F90

[MinsukJi-NOAA]

Description
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relevant motivation and context. List any dependencies that are required for
this change.

Fixes # (issue)

How Has This Been Tested?
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Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[MinsukJi-NOAA]

CI tests passed: https://github.com/NOAA-EMC/FMS/actions/runs/1369727893