Github actions: fix OpenMPI network issue when running make ptest

* Specify the loopback interface: Explicitly instruct Open MPI to use
  the local loopback interface (lo0) for communications by setting the
  OMPI_MCA_btl_tcp_if_include environment variable. In your terminal
  (e.g., zsh or bash), run the following command:
  + export OMPI_MCA_btl_tcp_if_include=lo0
  Then, try running your MPI program again.

* Set a short temporary directory path: In some cases, long file names in
  the default temporary directory can cause issues on macOS. Setting the
  TMPDIR environment variable to a shorter path like /tmp can help:
  + export TMPDIR=/tmp
  After setting this, try running your MPI program.

* Error message:
  [iad20-eo1205-ccaaba69-b68d-4eae-afa9-dee869e099ae-2690965F61F0.local:90667]
ptl_tool: problems getting address for index 0 (kernel index -1)
  --------------------------------------------------------------------------
  You requested support for tool connections, but no available
  FAIL: nprocs=./pnetcdf-permute ---- pnetcdf-permute
  interfaces were found after applying any include or exclude directives:

    Include:    NULL
    Exclude:    NULL
    Available:

  Please adjust your include or exclude to allow selection of an
  available interface.

Author: wkliao

.github/workflows/main.yml

@@ -192,6 +192,11 @@ jobs:
         - name: make ptests
           run: |
             cd ${GITHUB_WORKSPACE}
+            if test "${{ matrix.mpi_vendor }}" = "OpenMPI" ; then
+                # OpenMPI hacks when running in parallel on MacOS
+                export OMPI_MCA_btl_tcp_if_include=lo0
+                export TMPDIR=${RUNNER_TEMP}
+            fi
             make -s LIBTOOLFLAGS=--silent V=1 ptests
 
         - name: make distcheck