fix(applications): add ghostscript to print service packages

Selecting the print service installs cups, system-config-printer and
cups-pk-helper, but not ghostscript. cups relies on ghostscript for the
PDF/PostScript rendering filter, so driverless (IPP Everywhere) print
jobs fail out of the box with:

  cfFilterGhostscript: Unable to launch Ghostscript: gs: No such file or directory

Add ghostscript to the package list and cover it with a regression test.

Closes #4595

archinstall/applications/print_service.py

@@ -9,7 +9,7 @@ if TYPE_CHECKING:
 class PrintServiceApp:
 	@property
 	def packages(self) -> list[str]:
-		return ['cups', 'system-config-printer', 'cups-pk-helper']
+		return ['cups', 'system-config-printer', 'cups-pk-helper', 'ghostscript']
 
 	@property
 	def services(self) -> list[str]:

tests/test_applications.py

@@ -0,0 +1,7 @@
+from archinstall.applications.print_service import PrintServiceApp
+
+
+def test_print_service_includes_ghostscript() -> None:
+	# cups only ships the PDF/PostScript rendering filter through ghostscript,
+	# so driverless (IPP Everywhere) printing fails without it.
+	assert 'ghostscript' in PrintServiceApp().packages