[BUG] PERMAS .gz extension does not create zipped file

[martin-bernhard]

Describe the bug
The export to the PERMAS file format supports the two extensions *.dato.gz and *.post.gz but does not create a zipped version of the ASCII file formats *.dato and *.post.
I was expecting the same behaviour like it is implemented for NETGEN.

To Reproduce
Convert the test file box.med into PERMAS file box.post.gz.
meshio convert box.med box.post.gz

Diagnose
The output is not a zipped mesh file, but a simple ASCII file only.