Issues with doc/scripts/GMT_movie_progress.sh on Windows

**Description of the problem**

This test often fails with something like:

```125/1103 Test #126: doc/scripts/GMT_movie_progress.sh ............***Failed 20.06 sec
Set GMT_SESSION_NAME = 8917
GPL Ghostscript 9.50: Unrecoverable error, exit code 1
```

When the failing tests are rerun, it fails twice more because the temporary assembly directory (here `/tmp/junk`) only gets deleted when the commands all run successfully:
```
The following tests FAILED:
126 - doc/scripts/GMT_movie_progress.sh (Failed)
Errors while running CTest
+ ctest --output-on-failure --force-new-ctest-process -j4 --timeout 480 --rerun-failed
Test project D:/a/gmt/gmt/build
Start 126: doc/scripts/GMT_movie_progress.sh
1/1 Test #126: doc/scripts/GMT_movie_progress.sh ...***Failed 1.70 sec
Set GMT_SESSION_NAME = 53562
Error: ERROR]: Working directory /tmp/junk already exist and -Z was not specified - exiting
ERROR: D:/a/gmt/gmt/build/test/gmtest:82
memtrack errors: 0
exit status: 1
```
Is there a way to proceed with the cleanup if -Z is set but the script does not execute successfully?