g.proj: fix wkt output on Windows

[petrasovaa]

This added minimal test of g.proj -w to see whether it fails on Windows and then I added the fix suggested in #1955.

[petrasovaa]

Windows test before the change:

Running .\general\g.proj\testsuite\test_g_proj.py...
========================================================================
F
======================================================================
FAIL: test_wkt_output (__main__.GProjWKTTestCase)
Test if g.proj returns WKT
----------------------------------------------------------------------
Traceback (most recent call last):
  File "etc\python\grass\gunittest\case.py", line 1390, in assertModule
    module.run()
  File "etc\python\grass\pygrass\modules\interface\module.py", line 806, in run
    self.wait()
grass.exceptions.CalledModuleError: Module run `g.proj datum_trans=0 -w` ended with an error.

The subprocess ended with a non-zero return code: 32[21](https://github.com/OSGeo/grass/actions/runs/7215310826/job/19659296500#step:9:22)[22](https://github.com/OSGeo/grass/actions/runs/7215310826/job/19659296500#step:9:23)6[35](https://github.com/OSGeo/grass/actions/runs/7215310826/job/19659296500#step:9:36)6. See errors above the traceback or in the error output.

After the fix it runs:

Running .\db\db.copy\testsuite\test_dbcopy.py...
Running .\db\db.describe\testsuite\test_dbdescribe.py...
Running .\general\g.list\testsuite\test_g_list.py...
Running .\general\g.proj\testsuite\test_g_proj.py...
Running .\general\g.region\testsuite\test_g_region.py...
Running .\general\g.remove\testsuite\test_g_remove.py...
Running .\general\g.rename\testsuite\test_overwrite.py...