users-guide: fix incorrect ghcappdata folder for unix and windows

Thank you for your contribution to GHC!

Please take a few moments to verify that your commits fulfill the following:

• are either individually buildable or squashed
• have commit messages which describe what they do (referring to [Notes][notes] and tickets using #NNNN syntax when appropriate)
• have added source comments describing your change. For larger changes you likely should add a [Note][notes] and cross-reference it from the relevant places.
• add a testcase to the testsuite.

This should fix #21941 (closed) @sheaf