Fix test_mpp_nesting unit test

[laurenchilutti]

Description
When testing with intel ifort and ifx, using the flags -O0 -g -check all we notice that the three test_mpp_nesting tests fail. The failure was due to accessing an unallocated variable. Moving some calls inside of the if(ANY(my_pelist(:)==mpp_pe())) section has resolved this issue.

Fixes #1337

How Has This Been Tested?
tested on Amd development machine with intel oneapi ifort and ifx

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