Loosen platformdirs dependency (#1843)

4.x is backwards compatible with 3.x except that site_cache_dir has
moved to /var/cache. Vorta doesn't use this.

https://github.com/platformdirs/platformdirs/releases/tag/4.0.0

setup.cfg

@@ -37,8 +37,8 @@ package_dir =
 include_package_data = true
 python_requires = >=3.8
 install_requires =
-  platformdirs >=3.0.0, <4.0.0; sys_platform == 'darwin'  # for macOS: breaking changes in 3.0.0,
-  platformdirs >=2.6.0, <4.0.0; sys_platform != 'darwin'  # for others: 2.6+ works consistently.
+  platformdirs >=3.0.0, <5.0.0; sys_platform == 'darwin'  # for macOS: breaking changes in 3.0.0,
+  platformdirs >=2.6.0, <5.0.0; sys_platform != 'darwin'  # for others: 2.6+ works consistently.
   pyqt6
   peewee
   psutil