Add a test to make sure PyGMT works with paths that contain non-ASCII characters

[seisman]

Description of proposed changes

This PR adds a new test to check if PyGMT works on a user account that has non-ASCII characters (e.g., Chinese characters). The issue is initially reported in #3279.

It turns out GMT and PyGMT work well on Linux/macOS, but don't work on Windows. On Windows, the errors are like:

gmtset [DEBUG]: gmtlib_get_graphics_item: Fig: 29 Subplot: 2 Panel: () Inset: 0
gmt_mkdir (intermediate) error: Invalid argument
gmt_mkdir (intermediate) error: Invalid argument
pygmt-session [DEBUG]: GMT_DATA_SERVER is oceania
pygmt-session [DEBUG]: Download remote file http://oceania.generic-mapping-tools.org/gmt_data_server.txt for the first time
pygmt-session [INFORMATION]: Downloading file http://oceania.generic-mapping-tools.org/gmt_data_server.txt ...
pygmt-session [DEBUG]: Failed to release lock (Error <158>: The segment is already unlocked.

)
pygmt-session [DEBUG]: Delete C:\Users\RUNNER~1\AppData\Local\Temp/gmt_data_server.txt.download
pygmt-session [DEBUG]: Load contents from (null)/gmt_data_server.txt
pygmt-session [DEBUG]: GMT_DATA_SERVER is oceania
pygmt-session [DEBUG]: Download remote file http://oceania.generic-mapping-tools.org/gmt_hash_server.txt for the first time
pygmt-session [INFORMATION]: Downloading file http://oceania.generic-mapping-tools.org/gmt_hash_server.txt ...
pygmt-session [DEBUG]: Failed to release lock (Error <158>: The segment is already unlocked.

There are two main issues:

• gmt_mkdir reports errors "Invalid argument"
• The file path (null)/gmt_data_server.txt is incorrect, which means GMT->session.USERDIR=NULL

It's because when gmt_mkdir fails, GMT frees GMT->session.USERDIR (https://github.com/GenericMappingTools/gmt/blob/1c8a78b0613a227f406303930ebcf7238ad3401d/src/gmt_init.c#L3826). ChatGPT told me that the mkdir function on Windows doesn't support multi-byte characters. So I guess that's the reason and the test is skipped on Windows (I may find some time debugging this in the future but not now).