Passing through HOME environment variable in tox environments

[matt-graham]

We seem to be getting intermittent failures in the tox test and docs environments due to the lack of a HOME variable being set with the tox environment which is causing an error on importing dxh (and thus importing some dolfinx modules):

[fv-az881-524:03933] Error: Unable to get the user home directory
[fv-az881-524:03933] Error: Unable to get the user home directory
--------------------------------------------------------------------------
It looks like opal_init failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during opal_init; some of which are due to configuration or
environment problems.  This failure appears to be an internal failure;
here's some additional information (which may only be relevant to an
Open MPI developer):

  mca_base_var_init failed
  --> Returned value -1 instead of OPAL_SUCCESS
--------------------------------------------------------------------------
--------------------------------------------------------------------------
It looks like MPI_INIT failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during MPI_INIT; some of which are due to configuration or environment
problems.  This failure appears to be an internal failure; here's some
additional information (which may only be relevant to an Open MPI
developer):

  ompi_mpi_instance_init: opal_init_util failed
  --> Returned "Error" (-1) instead of "Success" (0)
--------------------------------------------------------------------------
--------------------------------------------------------------------------
It looks like MPI_INIT failed for some reason; your parallel process is
likely to abort.  There are many reasons that a parallel process can
fail during MPI_INIT; some of which are due to configuration or environment
problems.  This failure appears to be an internal failure; here's some
additional information (which may only be relevant to an Open MPI
developer):

  ompi_mpi_init: ompi_mpi_instance_init failed
  --> Returned "Error" (-1) instead of "Success" (0)
--------------------------------------------------------------------------
*** An error occurred in MPI_Init_thread
*** on a NULL communicator
*** MPI_ERRORS_ARE_FATAL (processes in this communicator will now abort,
***    and MPI will try to terminate your MPI job as well)
[fv-az881-524:03933] Local abort before MPI_INIT completed completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!

From testing locally, setting passenv = HOME in the tox configuration to pass through the HOME environment variable seems to fix the issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.1%. Comparing base (63d17ab) to head (172a552).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #23   +/-   ##
=====================================
  Coverage   97.1%   97.1%           
=====================================
  Files          1       1           
  Lines        201     201           
  Branches      40      40           
=====================================
  Hits         195     195           
  Misses         4       4           
  Partials       2       2           

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[samcunliffe]

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